I know you are looking for magical information with this question my friend, but unfortunately there is no way to know for certain if your woman is faking an orgasm or not.
This is because there is no for certain physical manifestation of a woman's orgasm. Sometimes her nipples may "peak" and other times they may not. Sometimes she may get a sexual "flush" over her abdomen and other times she may not.
If you do suspect your woman is faking I do not suggest asking her because you will probably not get a straight answer anyway and she may be quite upset by this question.
Instead think about the reasons why she may be faking her orgasm in the first place. I can think of four reasons.
1. She is bored of having sex with you and just want it to get over. Hopefully this is not the reason. Although it may be understandable in some particularly long sessions. You should consider that many women cannot orgasm from penetration alone.
2. She may not think you are willing to expend the effort it takes to really make her have an orgasm (i.e. she may only orgasm by oral sex for 20+ minutes.)
3. She doesn't want to hurt your feelings because she's not having an orgasm.
4. She is trying to compete with your other sexual partners. She wants to make sure that she is the most exciting and sexual partner you have had so she fakes an orgasm every time so you feel she is more exciting in bed.
If you suspect her of faking an orgasm for any of these reasons try the "delayed orgasm" trick as a test. Tell her that you heard that if she delays her orgasm as long as she can while you are going down on her that it will make it the most intense orgasm she's ever had. This will free her from all of the problems above (except #1, if that's the problem you may wish to find a new girlfriend.) This will let her have an orgasm naturally if she's been faking it for reasons 2 through 4.
