WordNet sense 1 (having keenness and forcefulness and penetration in thought, expression, or intellect):

trenchant

WordNet sense 2 (having the capacity for thought and reason especially to a high degree):

intelligent

WordNet sense 3 (diligent and thorough in inquiry or investigation):

probing, inquisitory

WordNet sense 4 (serving in or intended for exploration or discovery):

explorative