Does WSL use LF line endings or CRLF line endings?

The question doesn't really have an answer, because operating systems don't use line endings, applications use line endings. Most OS APIs provide the contents of a file to an application as a continuous stream of bytes, not a collection of lines, so it is up to the application to read and write line endings according to whatever algorithm it wants.

The convention on Windows (and before that, MS-DOS) was for applications to indicate line endings with a CR LF pair, while the convention on Unix (and related systems such as Linux) was for applications to use just an LF.

Modern applications are generally capable of reading and writing either format - that includes Notepad in up to date versions of Windows - but may pick a default based on these historical conventions.

Since applications running under WSL are the same as they would be running under a real Linux system, they will probably default to LF.