How to measure the component value on a PCB?
No, this is generally not possible because of the rest of the circuit. If you have a schematic you may be able to analyze the circuit and figure out what the value is from the 'incorrect' reading, but that is not always possible, even under ideal conditions. By ideal, I mean that you have a perfect understanding of the circuit, how you measuring instruments work (for example the waveforms used to measure capacitance including the voltages on each range) and how parts such as the chips Nick mentions behave when not powered and subjected to those waveforms). If a much smaller and/or less accurate part is effectively in parallel it may be impossible to get an accurate number. 

The most reliable way is to remove the parts with a tweezer type desoldering tool and measure it, then replace. Some larger (0603 and up) resistors are still marked but there are many smaller resistors and most SMT capacitors that are not marked at all (photo from here).