A) Episode 23 and 47. In episode 23, Kagome found Kikyo first before Inuyasha, Kikyo made Kagome invisible to make sure that Inuyasha doesn't hear or see Kagome. But, as being invisible, Kagome watched the whole thing between Inuyasha & Kikyo.
Episodes 33 (Kagome's illusion of death - seeing Inuyasha & Kikyo together), 43, 109, 125, 150, 151, 154, 158,160,165, Final Act ep. 2,7,8,9 & 10 - these are the episodes that Kagome knows that Inuyasha went to go see or to find Kikyo, or thinking about Kikyo or talking with Kikyo about something.