Does anyone know how to get a watermark off of an old wood table top?

"When asked how to remove a large watermark from a wood table, Woodworkers Guild of America recommends placing a clean dish cloth over the affected area and running a warm (not hot!) iron over the cloth for 30-60 seconds, increasing the heat if necessary. Others recommend rubbing the area with a clean cloth dipped in alcohol (except on shellacked surfaces) or using a mixture of baking soda and toothpaste for the job. The truth of the matter is, however, that preventing watermarks on wood is much easier than removing them. Here's what the professionals recommend to keep wood surfaces beautiful and watermark-free:" Read more here: https://www.proreferral.com/hg/how-remove-and-prevent-watermarks-wood/

I just recently read that warm air from a hair dryer might help.

I read somewhere that bleach would do the trick... When the color is as you want it to be, use vinegar to stop the effect of the bleach. I would try it somewhere else before... Like under the table.

Mayonnaise. put a bit onto a rag...then gently apply the mayonnaise directly to the stained area.... Let it sit for at least an hour or as long as overnight..reapplying the mayonnaise if the initial coating dries out. If there is no mayonnaise in your fridge..petroleum jelly may be used ...the idea is for the oil in them to seep into the finish...and revive the area moisture has got to... If seeing some results but want to give this a try bringing cigarette ashes .... I read that the penetrating power of oil works best when combined with the abrasiveness of cigarette ashes... I have used also Toothpaste.. not the gel but the paste.. just a tad on a small area and rub gently... I use to refinish furniture and a old Auctioneer told me a few of his tricks.. Best Wishes...

Here are some different things to try

https://thesecretyumiverse.wonderhowto.com/how-to/7-easy-ways-remove-water-ring-marks-from-wood-furniture-0155738/

you might try mineral oil.

I have used toothpaste (must be paste, not gel) to successfully remove water marks on my dining table.

Sandpaper