@Apsco60If a ranger has survival skill expertise from rogue and is in his/her Favored terrain, do you double the proficiency twice? nope, double once

— Mike Mearls (@mikemearls) March 15, 2016

For any roll, your proficiency bonus can be added only once and multiplied only once (see PH, 173-4). #DnD https://t.co/mtnZl22y51

— Jeremy Crawford (@JeremyECrawford) March 21, 2016