While checking the version of SAPUI5 libraries on the ABAP stack is widely known, I could not find anything to check the version on the JAVA stack.
One way to see the version is to go to anything UI5 in portal and press CTRL+SHIFT+ALT+P. This will provide you an SAPUI5 version, only for the stack you indicated the libraries should be consumed from.
For finding the version on the ABAP stack, there are several posts letting you know you can use the following URL:
But for the JAVA stack, I had to open an incident to find out there is a URL for that also:
We have found that while we consume the libraries from the ABAP stack, we build our theme for the FFP on the JAVA stack and if the versions are not kept in sync, we see inconsistencies in the theme.