Can I take a bicycle on the train from CDG to Nancy?
Some TGV trains sell an option of adding on a bicycle surcharge of 10€ when making your reservation online (when available for that train and not already sold out, must be done when booking. Bike spaces are not available for all TGV train times for a given route, only some).
By the way, there are no direct trains from CDG to Nancy. The direct trains from Paris to Nancy leaves from Gare de l'Est, iare TGV INOUI trains and some offer a few bike spaces (when booked ahead of time & subject to availability). If you manage to secure a bike reservation then your seat will be close to the bicycle parking on board and you won't have to disassemble the bike.
The French version of the SNCF page describes this. (The English version is scant on details.)