whether it is necessary to do seperate electronic earthing for electronic devices?

Answer 1

Garuda's answer is right, but you must make sure that your office or household equipment is grounded indeed and the neutral wire is always properly connected - as there are instances when electricians taking short cuts sometimes do not use the neutral wire properly.

The ultimate ground is generally to a water pipe. In industrial installations there is generally a dedicated ground for the electrical systems and the intrinsically safe systems generally have there own dedicated ground.

http://www.hometips.com/articles/sunset_books/complete_wiring/circuits/electrical_grounding016.html

Answer 2

If the electronic gadgets you refer is a house hold or office equipment you need not have a dedicated earthing.
The 3 pin wall / plug socket (Phase + Neutral + Earthing) should serve the purpose of earthing electronic gadgets.

Answer 3

Yes. It is always safe and desirable to have separate earthing for electronic devices to protect it from power line disturbances.

In plants or big offices the practice is followed.

As it is not always possible to have separate earthing for electronic devices at home, we compromise there.