You won’t be able to get player autographs at the stadium.
Honestly, the best way to get player autographs used to be by writing the team and requesting them. Other than postage costs, it was free. As of a few years ago, this was the snail mail address for those kind of requests:
Dallas Cowboys
AT&T Stadium
One Legends Way
Arlington, TX 76011-6143
I have never been an autograph person but I have a friend who has used this address to request autographs and had some sent back. I think you have to include an envelope with postage, etc. You may want to visit the team's website. They have a fan link that have more info. Good luck.