Learn Dutch: Hij is benoemd tot het ambt, hetgeen veel verantwoordelijkheid betekent. - He is appointed to the office, which means a lot of responsibility.

Both hetgeen and wat translate to "which" when referring back to a complete preceding clause (here: the fact that he was appointed). However, hetgeen is highly formal and mostly found in written language or official contexts. In everyday speech, you would almost always use wat (..., wat veel verantwoordelijkheid betekent).

Is tot the standard preposition to use with benoemen?

Yes, benoemen tot is a fixed combination meaning "to appoint as" or "to appoint to". You'll often see it in formal contexts, like benoemd tot directeur (appointed as director) or benoemd tot burgemeester (appointed as mayor).

Why does the translation say "He is appointed" but the Dutch uses is benoemd instead of wordt benoemd?

Dutch distinguishes between the action of being appointed (worden) and the resulting state (zijn). Hij is benoemd means the appointment has already happened, and he is currently in that state. If you used Hij wordt benoemd, it would mean the appointment is happening right now. English often uses "is" for both.

What is the difference between ambt and kantoor if both mean "office"?