This is a Free Kick....
The Receiver catches the ball at the 2 and his momentum takes him into the EZ.
- The receiver runs around in the EZ and gets tackled in the EZ
R's ball at the 2.- The receiver runs around in the EZ and fumbles in the EZ where K recovers
TD for K- The receiver take a knee in the EZ thinking the play was dead since the ball crossed the goal line
R's ball at the 2- While the receiver is running around in the EZ R committs a holding foul in the EZ
Safety.What rule covers this?
Sorry, you need to do a little work yourself, rather than someone giving you ALL the answers. 
Check the rules on safeties, touchdowns and the momentum rule.
