I was just about to leave for office when I (had remembered/remembered) my briefcase. please tell me which verb is correct.

your sentence has no meaning.. what do you want to say

मैं बस आफिस के लिए निकलने ही वाला था जब मुझे अपना ब्रीफकेस याद आया। this is totally wrong sentence in hindi as well.

choose the correct verb from bracket.

your both sentence has no co relation or any sence.. and if u see as a separate sentence, you can write both had remembered and remembered as well.