Does a target of the scrying spell know that they were the target of the spell, either as the spell is being cast or after the target makes their saving throw?
The text of the spell seems to leave it ambiguous, perhaps deliberately (emphasis mine):
The target must make a Wisdom saving throw [...] If a target knows you're casting this spell, it can fail the saving throw voluntarily if it wants to be observed.
If it is ambiguous and thus left up to the DM, what would be other ways for the target to know that someone was casting scrying on them, while the spell is being cast? (As opposed to detecting the sensor, if and when the spell is successful.)