Learn Swedish: Kan tidsmaskinen förutsäga framtiden åt oss? - Can the time machine predict the future for us?

You would use a subordinate clause structure. It becomes Tänk om tidsmaskinen kunde förutsäga framtiden åt oss! Notice that we changed Kan to the past tense kunde to make it hypothetical, which is very common after Tänk om.

Why does the sentence use åt oss instead of för oss?

In Swedish, åt is often used when an action is performed on someone's behalf or as a service, taking a task out of their hands. The time machine is doing the work of predicting for them. För can also mean "for," but it generally points to a recipient of a physical gift or someone affected by an emotion.

Is förutsäga a separable verb? Could I split it into säga förut?

No, förutsäga is an inseparable compound verb. While Swedish has many phrasal verbs where a particle comes after the verb, förutsäga is locked together as a single word in all tenses.

Could we use the verb spå instead of förutsäga here?

You could, but it changes the tone. Förutsäga sounds more analytical, logical, or scientific, much like "forecast" or "predict." Spå has a mystical connotation, like telling fortunes or reading tea leaves. Since we are talking about a machine, förutsäga usually fits better.