Is my current transformer rated for 11kV Tranmission line?
How do I know if will be safe on an 11kV line


It won't be safe so don't even think about it. If the technical spec states a limit of 3kV then that's its limit.

My recommendation - keep searching for what you want and do not exceed that voltage rating on the data sheet. Any CT you choose should be from a supplier you can believe in or has demonstrably adequate quality standards.

11kV is very dangerous stuff.