My question is :
1) If i measure the 50 ohm load using handheld vector analyzer, do I need to calculate the return loss or just direct take the reading?
you can show RL through VNA menu, but if your VNA doesn't have it you can calculate it
2) What is the pass fail criteria for 50 ohm load? does the impedance has range?
it depends on your circuit pass/fail criteria for which you're planning to use that dummy load.
For example if your circuit needs VSWR < 1.1 then pass/fail criteria is VSWR < 1.1.
3) Does the frequency range impact the impedance?
yes, every frequency has it's own impedance
Also note that VSWR is not the same within some frequency bandwidth. This is a curve.
4) while measuring the 50 ohm load, which measurement i need to refer to? VSWR or smith chart?
it depends on your device requirements, for which you're planning to use that dummy load
My goals is I need to make sure the 50 ohm load terminator is in good condition.
it depends on your own requirements for dummy load terminator.
If you're just want to load some amplifier output, there is no need for precise impedance match. For such purposes you can assume that terminator is good when it's VSWR < 1.1 and assume that terminator is acceptable when VSWR < 1.5.
The terminator VSWR should not exceed 2.618 which is a threshold level for 3 dB bandwidth.
But if you're want to use terminator for VNA calibration or precise impedance measurement, then your terminator needs much better precision, for example at least VSWR < 1.01 or better.