Real, fake? Some ways are easier to tell than others. Orgasms in women aren't easy to determine sometimes, that much is for sure.
The cl*t orgasm is probably the easiest to determine if it is real or not. The cl*t will be incredibly sensitive to the touch directly after she comes - she may move your hand away, or move to avoid any more contact to it. If you try to touch it or rub it you'll get a reaction similar to what would happen if you came, and your gf wanted to rub the head of your d*ck right afterward. It is an uncomfortable sensitivity.
The inside orgasm - not so easy to tell. When she comes the contractions on the inside will be involuntary, rhythmic and deep - the same sort of pulsing your d*ck does just before you ejaculate. The trick here is that women can fake that with some well timed kegels and heavy breathing/thrashing about.
Squirting is hard to fake. The real kind, anyway. Most of the stuff you see on porn is fake. If it is a steady stream of liquid in a nice straight stream equaling roughly a twenty liter bottle full, it is not the real deal. That is a porn chick pissing for your entertainment pleasure. The real deal is a gush that she has no control over - no more that you do over your own ejaculation. You aren't 'peeing out' your come, nor are you 'peeing out' a liter of it, and when a chick squirts for real - neither is she. It is propelled out of there by some powerful force. It is rarely a single stream, and not much more than an ounce or two - it is like shaking up a soda and popping the top. Messy, wonderful.