Hi. I have colonoscopy fri. Due to stomach pain I've eaten nothin for a no. Of days. Will I still have to stay off work when I take prep the day before?

Probably. You will still need to do the prep in order to have a completely cleaned out colon. If a polyp or something else is seen and a biopsy is needed then electro cautery is used and any residual gas in the colon from an incomplete prep may be ignited if you are a methane producer. But if you have not eaten much then the prep may not be, shall we say, as productive, but it would still be effective.
Yes. Depending on where and what you do for work. You will be visiting the john multiple times as the prep clears out your bowels. This will be difficult and potentially socially uncomfortable depending on who is around you not to mention potentially very unproductive. Oh, and you may want to wear dark pants that day.