I have a double knobs hot and cold. It just started dripping. How do I fix it?

What side's dripping? Hot or cold?
Shut the water off to the tap that's leaking and remove the handle and cartridge. Check the cartridge for any trash. Now place a pan over the tap and turn the water on to flush out the supply and open valve body. Reassemble and test. Drip gone? Good luck, Tom

How do I take off the cartridge?

Remove the screw and pull off handle assembly.
Turn off shut off valves underneath the sink.
Remove retainer clip (copper horseshoe shaped clip) and pull out cartridge with channel locks, pliers, or cartridge puller. Lube new cartridge with silicone jel and
Insert the cartridge with hole on the stem facing the 6 o'clock position, or down in a tub/shower.
Reinsert retainer clip and screw in handle assembly, followed by the cap or insert button. Turn water back on under sink. My company uses Moen valves on all their new construction. Moen makes a "cartridge puller" That will get those stubborn cartridges out of the valve body if you have a problem.