Same word as make sure:

catch on, check, check out, check up on, confirm, determine, dig, discover, divine, double-check, establish, eye, eyeball, find out, fix, get down cold, get down pat, get hold of, get it down, get the hang of, identify, learn, learn the ropes, look-see, make certain, make sure, peg, pick up on, pick up, read, see, settle, size, size up, tell, verify