My whirlpool dryer, Model # LGR7646EQ2 has just stopped drying. Ity still spins but does not have any heat. It is a gas dryer. What part or parts would I ned to fix this

I would check the thermostats (regular and hi-limit) and the flame sensor, first. All are fairly inexpensive and common problems. Less common issues are the igniter and the solenoid for the gas valve. If it starts to heat, then stops after 10 minutes or so, look at the dryer coils. I would check each of them in that order (unless you have the last problem).
A good parts supply house (and many online parts supply sites) will have good diagrams. You can order online or find suppliers in most areas in the Appliances-Parts section of the phone book.

Http://www.applianceaid.com/gas_dryer.html#noheat