How do i unlock Wotlk Instances?

Im at ilvl 120, what do i need to do to unlock the nexus and other instances so i can start lvl grinding my monk?

The iLvl doesn’t matter with dungeons (except Cata). You have to be at 70 to queue for Utgarde Keep and the Nexus (or 71, I forget which).

69 actually

Rather, I think they might be queueable at 68, but the random dungeon queue doesn’t open until 69

Correct. You can specifically queue for UK at 68, but RDF is open at 69 or 70.