For the record, I did check the trick book, and the only thing I found that said Footplant was a Lip trick performed by pressing RB and X at the top of a lip. This is not the trick they were looking for and you can not do a grind after this trick.
I did figure it out though. It's not in the trick book, but to do a footplant the way that the want you to, skate on a flat surface ollie and hold RT and X until you hit the ground. You will put your foot on the ground and then jump back on your board. Do this near a grindable surface during the own the lot activity and you will complete what they are looking for.