You don't need to know it, you can get a keycard :P
Spoiler
Go to the SCI0 room, and LOOK MONOLITH. Then DANCE. TAKE the CARD and leave. You can use that on the slot to get to the advanced room.
Other possibiity:
Spoiler
Go to the LEC-Room (Monkey Island2- Style), open the window, affix the mirror to the monkey, look into the Barrel, get the lens, use the lens on the monkey's arm, and finally take a note with the keycode out of the hole the ray has burnt.
That's much easier than Dragon's solution, don't you think? ;)