clock in vs clock on

clock in and clock on both are verbs.

Word	Noun	Adjective	Verb	Adverb
clock in	No	No	Yes	No
clock on	No	No	Yes	No

As verbs, clock in and clock on are synonyms defined as:

Other synonyms of clock in include punch in.

clock in (verb)	clock on (verb)
register one's arrival at work	register one's arrival at work