Someone I know recently died by killing himself. I don't know if he is going to Jannah or not, that's is why I wonder if he can see and hear us now.
There is no clear evidence as to whether the dead can hear or see those who are alive or not. There is evidence that certain incidents took place, or still take place, where the dead can hear those who are alive, but the opinion is that such incidents are either specific to the Prophet ﷺ or specific to a time or place.
The Qur'an compares the disbelievers to the deceased in their refusal to listen to the Prophet ﷺ:
إِنَّكَ لَا تُسْمِعُ الْمَوْتَىٰ وَلَا تُسْمِعُ الصُّمَّ الدُّعَاءَ إِذَا وَلَّوْا مُدْبِرِينَ
Indeed, you will not make the dead hear, nor will you make the deaf hear the call when they have turned their backs retreating.
It is a figure of speech that their deafness is likened to that of those who are dead, which means the dead do not normally hear. In another verse, Allah draws parallels between the believers (the living) and the disbelievers (the dead):
وَمَا يَسْتَوِي الْأَحْيَاءُ وَلَا الْأَمْوَاتُ ۚ إِنَّ اللَّهَ يُسْمِعُ مَن يَشَاءُ ۖ وَمَا أَنتَ بِمُسْمِعٍ مَّن فِي الْقُبُورِ
And not equal are the living and the dead. Indeed, Allah causes to hear whom He wills, but you cannot make hear those in the graves.
Then the verse, in a similar fashion to the previous verse in 27:80 likens the disbelievers' unwillingness to listen to the deafness of the dead. However, in a hadith narrated by 'Umar ibn al-Khattāb after the Battle of Badr, the Prophet ﷺ talked to the deceased among the disbelievers in their graves, and he told 'Umar that they could hear him:
عَنْ أَنَسٍ قَالَ كُنَّا مَعَ عُمَرَ بَيْنَ مَكَّةَ وَالْمَدِينَةِ أَخَذَ يُحَدِّثُنَا عَنْ أَهْلِ بَدْرٍ فَقَالَ إِنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم لَيُرِينَا مَصَارِعَهُمْ بِالأَمْسِ قَالَ
هَذَا مَصْرَعُ فُلاَنٍ إِنْ شَاءَ اللَّهُ غَدًا
قَالَ عُمَرُ وَالَّذِي بَعَثَهُ بِالْحَقِّ مَا أَخْطَئُوا تِيكَ فَجُعِلُوا فِي بِئْرٍ فَأَتَاهُمُ النَّبِيُّ صلى الله عليه وسلم فَنَادَى
يَا فُلاَنُ بْنَ فُلاَنٍ يَا فُلاَنُ بْنَ فُلاَنٍ هَلْ وَجَدْتُمْ مَا وَعَدَ رَبُّكُمْ حَقًّا فَإِنِّي وَجَدْتُ مَا وَعَدَنِي اللَّهُ حَقًّا
فَقَالَ عُمَرُ تُكَلِّمُ أَجْسَادًا لاَ أَرْوَاحَ فِيهَا فَقَالَ
مَا أَنْتُمْ بِأَسْمَعَ لِمَا أَقُولُ مِنْهُمْ
It was narrated that Anas said: "We were with 'Umar between Makkah and Al-Madinah when he started to tell us about the people of Badr. He said that the Messenger of Allah showed them the day before where they [the disbelivers] would fall. He said:
This is the place where so-and-so will fall tomorrow if Allah wills.
'Umar said: 'By the One Who sent him with the truth, they did not miss those places. They were placed in a well and the Prophet came to them and called out:
O so-and-so son of so-and-so! O so-and-so son of so-and-so! Have you found what your Lord promised to be true? For I have found what Allah promised me to be true.'
'Umar asked the Messenger of Allah: 'Are you speaking to bodies in which there are no souls?' He said:
You do not hear what I say any better than they do.'"
The majority of scholars that this incident was specific to the Prophet ﷺ on the day of Badr and only to the disbelievers. There is another hadith that may also be contextual to any person at the time one is being placed in one's grave, being able to hear the footsteps of one's friends:
عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ نَبِيَّ اللَّهِ صلى الله عليه وسلم قَالَ: إِنَّ الْعَبْدَ إِذَا وُضِعَ فِي قَبْرِهِ وَتَوَلَّى عَنْهُ أَصْحَابُهُ
Anas ibn Malik reported that Allah's Apostle (ﷺ) said: When the servant is placed in his grave and his friends retrace their steps.
Abu Huraira in the hadith about what happens to the soul of a believer after it ascends to heaven:
فَيُسْأَلُ: مَا فَعَلَ فُلَانٌ؟ مَا فَعَلَ فُلَانٌ؟
Then he is asked [by the souls of one's relatives]: "What happened to so-and-so? What happened to so-and-so?"
If the relatives of the deceased could see and hear their relatives, they would not have had the need to ask about their well being. There is a weak hadith that is widely circulated about the deceased returning the greetings of those who pass by their graves, but it cannot be used as proof:
ما من عبد يمر بقبر رجل كان يعرفه في الدنيا فيسلم عليه إلا عرفه ورد عليه السلام
Anytime a servant [of Allah] passes by the grave of a man that he knew in this world, and he sends his salām (greetings) to him, he [the deceased] would recognize him and return his salām.
The conclusion is we do not know one way or the other, but a higher number of scholars lean towards the inability of the deceased to hear or see.
In the name of God, the Beneficent, the Merciful
All praise and thanks are due to God, and peace and blessings be upon His Messenger.
Q-1: Can the dead see us?
No, the dead cannot see us, they are in purgatory as per God Almighty Said:
”Nor are the living and the dead equivalent. God makes those who prefer listen. You cannot make those in their graves listen." [Qur'an 35:22]
Here it means that they (their spirits) cannot see us not hear us, just like how we can not hear them nor see them. But, if God if you go to a graveyard and you say to a good believer, then God will Make him/her to hear you, but if you use abusive words against a righteous believer, then God will forbid him to hear what you tell him/her.
Q-2: Can the dead hear us?
Answer: If God wills, He can Make the one who killed himself hear you. See:
The Prophet (peace and blessings be upon him) said, ”If a Muslim were to pass by the grave of his believing brother whom he used to know in this world and greet him, the latter would recognize him and would return the same.’“
The Prophet further taught us to visit the graves of our relatives and friends and offer greetings by saying, “Greetings of peace be unto you, O the believers dwelling in these residences; with God’s Leave, we will also be joining you in the near future; may God forgive us, you, and all Muslims“ (Muslim)
In your case, that someone you knew died, you don’t offer him or her prayers for mercy and forgiveness as per the Hadith:
It was narrated that Jaabir ibn Samurah (may God have mercy on him) said: A man who had killed himself with a broad arrow-head was brought to the Prophet (peace and blessings of God be upon him) and he did not offer the funeral prayer for him, rather you must do what he needs.
Because, this is a major sin. But that doesn’t put him beyond the pale of Islam like the sin of disbelief.
The Prophet of God ￼ has said “If somebody commits suicide with anything in this world, he will be tortured with that very thing on the Day of Judgement” (Sahih Bukhari)
But, if God wishes, He May forgive him and enter him in Paradise. Or, first in Hell and then in Paradise.