The use of the interrogative なに (what) + か can mean “something” or “anything” :

何か飲みませんか = Would you like to drink anything/something?

(なにか/何か = anything/something. のみませんす/飲みませんます = would you like to drink. か = question marking particle)

だれ (who) + か can mean “someone” :

誰かをお待ちですか = Are you waiting for someone?

(だれか/誰か = someone. を = particle. お = honorific prefix. まちです/待ちです = wait. か = question marking particle)

なぜ (why, how) + か can mean “somehow” or “for some reason” :

なぜか町田さんがすきじゃありません = For some reason I don’t like Mr. Machida

(なぜか = somehow. まちだ/町田 = Machida. さん = Mr. が = ga particle. すきじゃありません = don’t like)

いつ (when) + でも = anytime, whenever

いつでもいいですよ = Whenever/anytime is good/ok

(いつでも = whenever. いい = good. です = is. よ = emphatic particle.)

なん (what) + でも = anything/everything/whatever

何でも食べますよ = I will eat everything

(なんでも/何でも = everything. たべます/食べます = will eat. よ = emphatic particle)

The general rule is : an interrogative + か will mean something, someone, sometime etc. but an interrogative + でも will mean anything/everything/whatever/anyone/whoever/anytime/whenever, depending on the interrogative word.