striking vs happening

striking and happening both are nouns.

Word	Noun	Adjective	Verb	Adverb
striking	Yes	Yes	No	No
happening	Yes	No	No	No

As nouns, happening is a hypernym of striking; that is, happening is a word with a broader meaning than striking:

Other hypernyms of striking include natural event, occurrence, occurrent.

striking (noun)	happening (noun)
the act of contacting one thing with another	an event that happens
the physical coming together of two or more things

striking (adjective)	happening (adjective)
having a quality that thrusts itself into attention
sensational in appearance or thrilling in effect