work on vs work at

work on and work at both are verbs.

Word	Noun	Adjective	Verb	Adverb
work on	No	No	Yes	No
work at	No	No	Yes	No

As verbs, work on and work at are synonyms defined as:

work on and work at: to exert effort in order to do, make, or perform something

work on (verb)	work at (verb)
shape, form, or improve a material	to exert effort in order to do, make, or perform something
to exert effort in order to do, make, or perform something