Shut off the hot water shut off to the sink and then take the flexible hose (from shutoff to faucet) and remove it from the faucet attachment and direct it into a bucket and then turn hot water shutoff back on for a second or two... if water flows strongly then issue is in the faucet. If water flows weakly then the issue may be at the shutoff itself. If issue at the faucet
then shut the hot and cold water shutoffs and remove the guts to the faucet. Then clean the guts/cartridge, etc, then pulse the hot water shutoff (make sure you reconnected it to faucet...
) on for a few seconds while covering the valve with a rag... is water strong flow? Then replace the parts and turn water back on. See if that resolves issue. If not, then may need to replace the cartridge/guts, etc. If issue is at the shutoff
then you would need to shut the cold water feed into the water heater and then drain the water pipes to the lowest sink in the house (turn on only hot side of 2 handle faucets... DO NOT open single handle valves). Then remove the stem assembly
from the shutoff (one at a time) and then pulse the water feed to the water heater for a second or two to send debris into a rag covering the shutoff. Then re-install stem and then test all and see how you did.
These are the first steps to take. Try them and let us know what you discover...