Saad,

It rather depends on the material that the hot plate is made of, how accurately you want to measure its temperature, and what temperature range this is working at.

Is it a big dumb block of metal at ambient (200 to 500K)?

(drill and tap a couple of holes, and then bolt a Pt100 in place - a stainless-steel encased Pt100 ought to do the trick)

Is it a small block of copper at cryogenic temperatures?

(use GE Varnish to stick down a T type thermocouple, insulated with cigarette paper)

Is it a lump of iron at ambient temperatures (and you don't care too much about accuracy)?

Thermally-conductive epoxy and a thermistor.

etc.

More details would help.

Thank you.