temperature of food in the microwave
Some microwaves (not many) include a temperature probe. If yours does not, no luck there.

Don't just stick in a thermometer, it will probably result in arcing and damage.

So, you're back to the olde-fashioned methods where the various stages (soft ball, hard ball, soft crack, hard crack) got their names from - drip some into cold water and see what happens to it, then microwave for some additional time, or don't - or use a stovetop and a pan and a thermometer (the microwave is a challenging heat source for candy-making.)