Advice on Selling Grandfather's DeVille

It’s not really a collector watch, your best is going to be to list on ebay no reserve with a low starting bid. The watch is called an “Omega De Ville Symbol” in two-tone from the late 80s or early 90s.

Quartz watches are not considered collectible. What should you ask for it? You’ll likely find yourself taking what you can get.

Take it to a quality jeweler in your area and ask if they can open it up to get the reference number off of the back of the case. The "reference number" is like the model number for that watch. Use that reference number to run a search on Ebay to get an idea of what they sell for, if you want to list it there.
Or....if you don't want to take it to a jeweler, you can just start searching Ebay using the key words that Dsio provided you in the 2nd post to this thread, until you find a listing that is an EXACT match for yours and then use that to research what the value range is on it.
Or.....and this is my advice......keep it as a nice momento of your grandfather. Without doing any research, I suspect the value on that watch is somewhere in the $100-$200 (USD) range. After shipping and Ebay's cut, it doesn't seem worth the hassle to give up something like that for that much money.
Good luck

The reference number may be in that booklet. As noted above, it’s not a model that most of the collectors on this site will have paid attention to. Do some research on eBay sales (not asking prices) and if someone makes you a reasonable offer, let it go. As you can see, it’s very dated and not something most people will find attractive, TBH.