My one handle shower assembly does not allow any hot water to flow. What needs to be repaired?

Clean Water Damage Atlanta

Hard to say with out knowing how old it is, manufacturer or style. New styles have a temperature limiting device to prevent scalds. If the faucet is newer and has recently been worked on this could be the problem. On older faucets it is possible that the hot water side is clogged. Does your hot water heater work. Has any work been done recently in your home.
If you update your question with more details, I will update my answer.
Mark

UPDATE: You are going to have to shut off water, dis-assemble, and figure out if hot water is making it to faucet or if it is a faucet issue. Might be best to hire a Handyman/plumber if you are not too handy!
Mark
Mark

Clean Water Damage Atlanta

If you have an anti scald mixing valve. The problem may be the anti scald pin that is stuck or plugged. Take it apart and clean it. Some valves come apart and some do not.

Clean Water Damage Atlanta

it is more than likely the cartridge in the faucet. you will need to kill the water to the faucet, take the cartridge out and go buy a replacement.