They are two ways to answer/interpret the question.

The first is: how much time are you "legally" entitled/required to take

The answer to this question will vary across country, university, and even how you are "employed" within a university. Even if this could be answered in general or for you specific situation, I am not sure it is helpful given the second interpretation.

The second is: how much time do PhD students actually take

This seems to me a more relevant question and is similar, if not identical, to: How hard do early-career academics in the United States work, really?. I believe that N-of-1 type answers are meaningless since I know people who takes zero vacation days and I know people who take in excess of 60 vacation days. The Sigma Xi society surveyed post docs and found that they take 12 vacation days a year on average. I provided details about this study in this answer of mine. I am not sure to the extent to which the vacation habits of post docs and PhD students are similar, but this is the only population study I am aware of.

They are two ways to answer/interpret the question.

The first is: how much time are you "legally" entitled/required to take

The answer to this question will vary across country, university, and even how you are "employed" within a university. Even if this could be answered in general or for you specific situation, I am not sure it is helpful given the second interpretation.

The second is: how much time do PhD students actually take

This seems to me a more relevant question and is similar, if not identical, to: How hard do early-career academics in the United States work, really?. I believe that N-of-1 type answers are meaningless since I know people who takes zero vacation days and I know people who take in excess of 60 vacation days. The Sigma Xi society surveyed post docs and found that they take 12 vacation days a year on average. I provided details about this study in this answer of mine. I am not sure to the extent to which the vacation habits of post docs and PhD students are similar, but this is the only population study I am aware of.

To the extent vacation habits of post docs and phd students are similar my answer about post docs might be helpful. Post docs take 12 vacation days a year on average.

They are two ways to answer/interpret the question.

The first is: how much time are you "legally" entitled/required to take

The answer to this question will vary across country, university, and even how you are "employed" within a university. Even if this could be answered in general or for you specific situation, I am not sure it is helpful given the second interpretation.

The second is: how much time do PhD students actually take

This seems to me a more relevant question and is similar, if not identical, to: How hard do early-career academics in the United States work, really?. I believe that N-of-1 type answers are meaningless since I know people who takes zero vacation days and I know people who take in excess of 60 vacation days. The Sigma Xi society surveyed post docs and found that they take 12 vacation days a year on average. I provided details about this study in this answer of mine. I am not sure to the extent to which the vacation habits of post docs and PhD students are similar, but this is the only population study I am aware of.