When you are on a profile in FamilySearch, go to the sources tab and then refresh your screen. A button will then appear [Get All Sources]. Click this, then wait until another little box pops up. When the box pops up, hit the copy button and then paste under sources on WikiTree.
I do suggest verifying all the sources look good prior to refreshing the screen. Sometimes you'll find outdated sources you can detach or sources that don't match the person (rare but it does happen).