1. -During(prep)- working(g), you should follow proper office procedures.
Is the above sentence grammatically correct?
Or should I replace the gerund with noun - 'work'?
Please guide me.
If you are dead-set on using a gerund, you could say:
When working, you should follow proper office procedures.
I'm not sure what the intended meaning might be. I wonder why "while at work" or "when working" is being used to qualify the statement. It's obvious that no one would be expected to follow proper office procedure at home.
The one you posted originally sounds wrong because following procedures is about what you have to do all the time while you are working. The two new examples you've found suggest a deviation from the work routine, either to take a break or surf the net.
I agree that 'During work' is as good as the other suggestions, at least I have no violent objections to it, except that it has a faintly unnatural twang. But for me they are all infected so to speak by the strangeness of the whole sentence which Suzi has highlighted.