We may be able to tell if they are stressed, which could be related to pain, depending on your viewpoint.

Here is a recent study of audible reactions plant can have to stress: https://www.cell.com/cell/fulltext/S0092-8674(23)00262-3

Do plants react to stress and harmful situations like infestation? Absolutely. Do they actually feel pain as we understand it? Probably not since they lack a nervous system.

This boils down to the question: What is pain?