you cant measure the capacitance in-circuit. I suggest you try a standard smd value of 100nF it wont cause any harm at all. Capacitance meter are not so common, you need to remove capacitor and measure it externally, not easy, plus risk of damage again for any one who tries. These are normally fixed in place by a little adhesive during manufacture. just try teh the standard it should work if everything else is okay.