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... learn, when a verb goes with Dativ and when with Akkusativ?

Use that rule with direct and indirect object as you already know.

Or in the words of the rule above, how does one know that ich is a undirect object for antworten while a direct object for fragen?

You just can imagine the Dativ concerning antworten in a way that someone gives information back to someone, and you reduce it from Antwort geben to antworten. But that's just a guess from my feel for language. A reply gives something back, so that may be your virtual direct object. The same goes with imponieren, "make a good impression on someone".