There's a big difference between a knob and a valve. Do you have a picture? But wherever lubricating oil would work, baby oil should work too. Temporary.
If you have a cartridge type faucet (pull/push for volume, twist for hot/cold), you want Silicone Grease: I called a DANCO sales rep because they make different types of grease and no one at Lowes could answer my questions. There are different types of grease out there for this stuff, and there's some confusion...you want the SILICONE for your cartridge faucet. The other type says "Waterproof." "Waterproof" is for static applications (regular old-school faucet washers and o-rings that are not subject to friction when in use.) Be careful, because the packages are identical except for the names. Anything other than silicone grease will wear away quickly during use and your problem will return. You're better off if you can take the cartridge out and grease the whole thing. Also, get yourself some cheap disposable latex gloves because this stuff is sticky!!! You will not wash it off of your fingers...it eventually wears off.