Hi @Ginette.C.407 ,
Thanks for reaching out to the Brightspace Community with your question.
Currently, the use of Turnitin is not supported within the Discussions tool. It's a great suggestion, and we encourage you to connect with the following PIE item to share details about your use case.
Turnitin discussions (D10034)
I'm sending along documentation for enabling Turnitin for Assignments, in case it's helpful😀