A weak or non-functioning sink sprayer is usually caused by mineral buildup in the sprayer head or a stuck diverter valve. Both fixes are simple.
Unscrew the sprayer head from the hose counterclockwise. Drop it into a bowl of undiluted white vinegar and let it soak for 30-60 minutes. Mineral deposits will dissolve and the spray holes will clear.
Rinse the sprayer head thoroughly and reattach it to the hose. Turn on the faucet and press the trigger. If the flow is restored, you're done.
If soaking doesn't restore adequate pressure, replace the sprayer head with a Danco universal sprayer head. If still no pressure, the diverter valve inside the faucet body may be stuck and needs cleaning or replacement.