Learn Finnish: Haluan tietää, voitko arvata vastauksen. - I want to know if you can guess the answer.

In English, we use 'if' or 'whether' for indirect questions. Finnish doesn't use a separate word for this. Instead, you just take the direct question (voitko, meaning 'can you?') and embed it into the sentence. It literally translates to 'I want to know, can you guess the answer.'

Could I use the word jos here to mean 'if'?

No, and this is a very common trap! The Finnish word jos is only used for conditional 'if' statements, like 'If it rains, I will stay home.' When 'if' really means 'whether' in an indirect question, you must use the -ko/-kö question ending attached to the verb.

Is the comma before voitko mandatory?

Yes! Unlike in English, Finnish grammar requires a comma to separate the main clause (Haluan tietää) from the indirect question clause (voitko arvata vastauksen).

Why does the word for answer (vastaus) have an -en ending here?

Vastauksen is the direct object of the verb arvata (to guess). Because the action is seen as complete (you are expected to guess the entire answer), the object takes the genitive-accusative ending -n. Notice that the word undergoes a stem change from vastaus to vastaukse- before adding the ending.