In al-Masjid al-Aqsa towards which direction for Namaz was used before the Kaaba in Mekka.
If you mean how would one pray in the Masjide al-Aqsa before Allah had given us the order to pray towards (al-Kaaba) al-Masjid al-Haram in verse (2:144) which was discussed in the verses around it (2:142-150)? Well look at how Muslims pray in the Masjid al-Haram these days and you'll have a hint of an answer. As the most interesting would be what is the exact direction there!.
You should know that the Masjid al-Aqsa was for the People in Medina in the totally opposite direction of the Masjid al-Haram so changing the qibla was as described in Quran not an easy act, as the information about this (new) revelation reached some of the sahaba just before prayer time as you may read in this hadith. Note the sahba (May Allah be pelased with them) who have been living next to our Messenger (peace be upon him) already knew about it and the first prayer which was prayed in this direction apparently was dhor/zohr prayer, there are several ahadith showing how some sahaba met -later- met others praying towards al-Masjid al-Aqsa and informed them and they turned in their prayer towards the right direction. According Imam al-Qurtubi a sahabi called Abu Said al-MU'alla أبو سعيد بن المعلى was the first who performed two rak'a towards al-Masjid al-Haram.
Of course for people living in Medina the direction was more or less towards a-Shaam -> Syria-Palestine before the revelation about the change came.
وقد جاء في هذا الباب أحاديث كثيرة ، وحاصل الأمر أنه قد كان رسول الله صلى الله عليه وسلم أمر باستقبال الصخرة من بيت المقدس ، فكان بمكة يصلي بين الركنين ، فتكون بين يديه الكعبة وهو مستقبل صخرة بيت المقدس ، فلما هاجر إلى المدينة تعذر الجمع بينهما ، فأمره الله بالتوجه إلى بيت المقدس ، قاله ابن عباس والجمهور
so this is my edition of the English translation according the Arabic text from above.
There are several other Ahadith on this subject. In summary, Allah's Messenger was commanded to face the Rock in Bayt Al-Maqdis (during the prayer) and he used to offer prayer towards it in Makkah between the two corners (of Ka
bah), so that the Kabah would be between him and Bayt Al-Maqdis8. When the Prophet migrated to Al-Madinah, this practice was no longer possible; then Allah commanded him to offer prayer towards Bayt Al-Maqdis
This means if the qibla was still in Masjid al-Aqsa people there would pray in any direction which leads towards the rock, as it is for the Kaaba in al-Masjid al-Haram.