Check
examine
review
investigate

And (there are duplicates-- I took them from multiple entries of Thesaurus.com):

audit, check out, delve into, dig, examine, explore, follow up, go into, inquire, inspect, investigate, look over, make inquiry, probe, prospect, research, scrutinize, sift, study, come across, delve, dig down, discover, expose, extricate, find, go into, inquire, look into, probe, prospect, research, retrieve, root, search, shake down, sift, uncover, unearth, analyze, burrow, delve into, dig into, examine, go into, hunt, inquire into, inspect, look into, probe, prospect, question, reconnoitre, research, scout, scrutinize, search, seek, sift, survey, test, tour, travel, traverse, try, analyze, catechize, examine, explore, feel out, go over, grill, hit, hit up, inspect, interrogate, investigate, knock, look into, probe, prospect, pry, query, question, request information, roast, scrutinize, search, seek, seek information, sift, study,  bug, buzz, candle, case, check out, check over, check up, consider, delve, dig, double O, examine, explore, eyeball, feel out, frisk, go into, inquire, inquisite, inspect, interrogate, listen in, look into, look over, look-see, make inquiry, muckrake, nose around, poke, probe, prospect, pry, question, read, reconnoiter, research, review, run down, scout, scrutinize, search, sift, slurp, spy, stake out, study, tap, wiretap..