"What, where, when?"

Translation: Was, wo, wann?

[FabioGardelli]

Why "wenn" for "when" is not correct?

[dragonzkiller]

"Wenn" means "if" or "when" as a conditional. So only when used like "When/if you go to the store, buy milk." A general idea is if you can replace "when" with "if," then the equivalent German word is "wenn." "Wann" is used for asking when something occured.

"When did you go to the store?" -> "Wann bist du zum Laden gegangen?" (asking for a time)
"When/if you go to the store, buy milk." -> "Wenn du zum Laden gehst, kaufe Milch."

Hope this helps!

[Ravestor]

That makes a lot of sense!
Thank you and have a lingot.

[TaraJ5]

Are wohin and woher also correct answers, since their translation to English is where?

[JameezDuol]

wo = where, wohin = where (to), woher = where (from)

[hedgehogEMD]

in the questions how do you interpret the wann as per drgaonzillers comment