Should a judge assume that any triggers not mentioned have been missed when providing a ruling?
Jason should feel free to ask questions that may reveal that a trigger was missed, or even to ask directly whether an ability triggered.
One kind of &quot;free information&quot; as defined in in section 4.1 of the tournament rules is

Details of current game actions and past game actions that still affect the game state.

This includes abilities that created continuous effects that still affect the game state, like the Prowess ability in the example would have if it triggered. That section of the rules then makes the following statements about judges and free information:


Players must answer all questions asked of them by a judge completely and honestly, regardless of the type of information requested. Players may request to do so away from the match.

Judges are encouraged to help players in determining free information

If anything, the last sentence seems to encourage Jason to ask whether a triggered ability triggered, if it affects his ruling.
Of course, if Jason's questions do remind the player of a triggered ability that they had in fact forgotten, Jason may have to make another ruling about whether the trigger actually counts as missed. But neither the possibility of giving that reminder nor the possibility of having to make that ruling should deter Jason from asking any questions that are relevant to the ruling.