Ok, maybe this will help, as I am experienced in anal play as I have been enjoying anal masturbation with my many dildos and butt plugs for years. My wife also likes to do me in the anus with my big dildos and likes to watch me when I insert the real big butt plugs. She says it is very erotic to see how they stretch my anus. I have had many "anal orgasms" while I or we play, this is an orgasm that is felt deep in the anus, most times quite intense, with intense body spasms. This occurs after prolonged anal play and is not the same as a penis orgasm, or prostate orgasm, as usually very little cum will run from the penis. Anyway, let's assume you are in a doggy stlye postion and your wife is behind you. As she inserts her finger or fingers, she should bend them a little downward toward your ball sac. She should feel a small walnut size knot, when she pushes on it you should feel this in your penis as well. It may feel like you need to pee, but as she continues to massage it, seminal fluid should start to run from your penis. If you are laying on you back then of course she has to bend her fingers up toward yor ball sac. Enjoy!!

Larry covered it... Depending upon the length of your wife's fingers she may have to really push up you... I'm in med school and I found when giving prostate exams I have to really push hard up towards the chest to get my finger in far enough to really feel the gland. On pushing on it... easy does it... It is very very sensitive... Have her start with more rubbing than actual pushing.