This question is a well-known riddle. Although at first glance it seems that the shirt only has holes for the head and arms, there is a surprising answer.

Answer to the riddle
If you look closely at the question, you can conclude that the shirt has at least four holes:

A hole for the head.

Two holes for the sleeves.

A hole for the waist.

Sometimes the holes can also be accompanied by buttonholes or other openings made by the fabric.

If you have a picture or a more detailed description of the shirt, I can give you a more accurate answer.