How do I tell a real woman from a transexual woman?

Well firstly you shouldn’t need to tell them apart and should just accept the lady for who she is. She is completely valid 

If this is for something else, it depends on how much they have transitioned. Their voice could give them away or possibly body shape. Face shape could also be a sign. 

I don’t want this to be used to against all the beautiful trans women out there. 

Well the jawlines or chins may be a bit different, they may have a somewhat male sounding voice, or may sound like a female, maybe more broad shoulders. Most trans women look slightly different than biological women unless they transitioned before puberty. 

By her Adams apple

Very few mtf trans people look like biological women. The only exceptions are those who've transitioned before puberty.

Date a girl you have known since middle school or if not then just don't get too attached to anyone until you've seen many childhood pictures and/or a birth certificate. 

.. I'm with you though, imagine the pain of wanting a family and putting time and effort in a relationship being lied to and deceived by this cruel and ill person because they consider themselves something they aren't. 

Turn them over and look at them.

Trannies have big heads with male brows; they also have big feet and huge hands; their voices are male, and if they destroyed their penis their fake vagina is made in the wrong place.

Please, their feeling down there is completely numb since their surgeons are quacks who are trannies themselves.  

Just say lines like that to every woman you meet.  A trans woman (who by the way IS a real woman) will bïtch-slap you, and rightfully so, while a cisgender woman will just call you a pig.

You could try not bothering?

Respect her identity and don't imply they aren't "real" women and maybe we'll tell you.