Same word as investigation:
analysis, case, delving, examination, exploration, fact-finding, gander, hearing, hustle, inquest, inquiry, inquisition, inspection, legwork, observation, observing, pike, probe, probing, quest, quiz, research, review, scrutiny, search, sounding, study, survey, surveying
analysis, case, delving, examination, exploration, fact-finding, gander, hearing, hustle, inquest, inquiry, inquisition, inspection, legwork, observation, observing, pike, probe, probing, quest, quiz, research, review, scrutiny, search, sounding, study, survey, surveying