I can find no RAW, or any rulings at all, that can help answer this question. That being said, the following is speculation based on the entry on PHB page 205 that details ‘The Weave’ of magic.

In conjunction with how Wizards learn their magic, and the knowledge of the Arcane arts and the understanding they must have of the Weave in order to cast such magic, we can assume that yes: A wizard would known when the magic he cast a few turns ago that affected the Weave in such a way as to turn an ally invisible has lost its effect and thus become inert. I think this particularly holds true for concentration spells where the Wizard is actively maintaining the alteration to the Weave in order to sustain an effect.

When the spell ends, either through the Wizard deciding to end it, the spell running its full duration, or something ending it prematurely, I have no reason to believe this would be lost on the Wizard in question.

I can find no RAW, or any rulings at all, that can help answer this question. That being said, the following is speculation based on the entry on PHB page 205 that details ‘The Weave’ of magic.

In conjunction with how Wizards learn their magic, and the knowledge of the Arcane arts and the understanding they must have of the Weave in order to cast such magic, we can assume that yes: A wizard would know when the magic he cast a few turns ago that affected the Weave in such a way as to turn an ally invisible has lost its effect and thus become inert. I think this particularly holds true for concentration spells where the Wizard is actively maintaining the alteration to the Weave in order to sustain an effect.

When the spell ends, either through the Wizard deciding to end it, the spell running its full duration, or something ending it prematurely, I have no reason to believe this would be lost on the Wizard in question.

I can find no RAW  , or any rulings at all, that can help answer this question. That being said, the following is speculation based on the entry on PHB pg. 205 that details 'The Weave' of magic.

In conjunction with how Wizards learn their magic, and the knowledge of the Arcane arts and the understanding they must have of the Weave in order to cast such magic; we can assume that yes: A wizard would known when the magic he cast a few turns ago that effected the Weave in such a way as to turn an ally invisible, has lost it's effect and thus become inert. I think this particularly holds true for concentration spells where the Wizard is ACTIVELY maintaining the alteration to the Weave in order to sustain an effect.

When the spell ends, either through the Wizard deciding to end it, the spell running it's full duration, or something ending it prematurely; I have no reason to believe this would be lost on the Wizard in question.

I can find no RAW, or any rulings at all, that can help answer this question. That being said, the following is speculation based on the entry on PHB page 205 that details ‘The Weave’ of magic.

In conjunction with how Wizards learn their magic, and the knowledge of the Arcane arts and the understanding they must have of the Weave in order to cast such magic, we can assume that yes: A wizard would known when the magic he cast a few turns ago that affected the Weave in such a way as to turn an ally invisible has lost its effect and thus become inert. I think this particularly holds true for concentration spells where the Wizard is actively maintaining the alteration to the Weave in order to sustain an effect.

When the spell ends, either through the Wizard deciding to end it, the spell running its full duration, or something ending it prematurely, I have no reason to believe this would be lost on the Wizard in question.