What is the french translation of “a work in progress” in the context of a person being a work in progress? Is it “un travail en cours?”
You could use something that doesn't literally translates as "work":
Je me construis encore
Je me cherche encore
Those are expressions way more used than "travail" when talking about yourself. Because it's not a "travail" you're constructing, you're constructing yourself. Work is more global in english, you can use it for "a work of art" for example, whereas in french you would more say "une oeuvre d'art".
If you really want to have this "work" nuance, you could maybe say:
Une oeuvre en réalisation.
It doesn't sound natural for me to say that I'm "un travail en cours" if I am talking about me being a work in progress. The closest I could think of in French would be to say that I'm working on myself, which would give:
Je travaille sur moi-même.
If you would like to just translate "a work in progress" when referring to yourself, I would then just say "un travail sur moi-même."