Well in skate 2 they created a new grinding system, it is very complicated but once you get it down you will look like a pro. Be sure to have your tennis shoe with +2 awesomeness equipped. Then you need unlock your board and learn how to ollie. Then you ride to mordor and go into the volcano through the impossible cave door. Then you will unlock hte Hoth mission, go on the mission with an immortal actor\and cut his stomach open for irony bonus, and take a nap inside him. When you wake up you will have gained ollieing powers for your skateboard. Then you must wander around the chinese country side and have an epic encounter with a cow and defeat him by milking him. When done, you will be thirsty. Go to the dinner and get milkshake and reflect on the days work. Go into a stranger's house kill them an d sleepin there bed.
Once you wake up you need sit down at the table with the pourage, right when you are about to bight in you will be warned my mr.ackbar that it's a trap then you will procede to the door and run from the bears that actually live in the house. You will end up in a city called weeds where you will be bucking barley all day, once you are done looking up what that means you will have learned how to grind! Then you must find an appropriate rail to ollie on to, the rail must be 78ft and 5.4 in. long, no more, no less. Once you found it you need to do a laser flip rodeo 5 onto the rail and balance on one wheel.
That is the only way to grind in skate 2 hope it helped.