Do characters know if someone else, who they can see, has failed a saving throw?

Do characters know if someone else, who they can see, has failed a saving throw?

In particular, let’s consider the following cases:

  1. a caster has cast a spell, that requires a saving throw, and that doesn’t require concentration, on an enemy (not a damaging spell, let’s consider the spell Command for example), at the moment of the cast, since this information can influence the strategy of the caster before the command is eventually executed;
  2. an ally is making a death saving throw, this can influence the priorities of the allied of that character.