observant vs observing

observant and observing both are adjectives.

Word	Noun	Adjective	Verb	Adverb
observant	No	Yes	No	No
observing	No	Yes	No	No

As adjectives, observant and observing are synonyms defined as:

observant and observing: quick to notice; showing quick and keen perception

observant (adjective)	observing (adjective)
paying close attention especially to details	quick to notice; showing quick and keen perception
(of individuals) adhering strictly to laws and rules and customs
quick to notice; showing quick and keen perception