This webpage provide some pieces of information.
Les TGV / INTERCITES / OUIGO ouverts à la réservation sont garantis pour des voyages jusqu'au 16 janvier 2020 inclus.
TGVs / Intercities / OUIGO trains still open to booking are warranted for travels up to 16 january included. So if you can book a ticket for your train, or if is still signaled as "complete", it is still expected to exist. Otherwise, it is flagged as deleted.
EUROSTAR / THALYS / TGV LYRIA , TGV FRANCE ITALIE or Transilien : you won't know before 5pm on the day before your travel. Transilien are local trains near Paris. For local trains trains, information is available on regional websites.
Nevertheless, on the same webpage, it is written:
Le trafic OUIGO sera fortement perturbé et des trains pourront être supprimés au plus tard 2 jours avant leur départ.
The OUIGO traffic will be heavily pertubed and trains could be cancelled up to 2 days before their start.
You may get a SMS or a mail from SNCF stating that your train has been cancelled, providing some alternatives (another train on another hour) or not.
Les informations sont disponibles chaque jour à 17h sur la circulation des TGV / Intercités / OUIGO des 2 jours suivants sur l’Assistant SNCF et le site SNCF.
Pieces of information are available every day at 17h about TGV / Intercités / OUIGO train moving within the next 2 days. Nevertheless, if you open the link, it is written:
Pendant toute la durée de la grève, l’information sur les trains du lendemain est disponible tous les jours à 17h sur l’Assistant et les outils d’information SNCF.
For the duration of the strikes, information regarding the train moving on the next days are available every day at 17h.
The french rail union Sud Rail issued a strike notice from 18 november 2019 to 18 january 2020 and a new one covering from 18 january to 18 march 2020. The law changed in 2007: the rail workers must individually signal whether they are on strike 48h in advance.. But they are allowed to stop working at any time in case of imminent danger capable of triggering accidents, deadly illness or illness implying a temporary or permanent inability to work.
If you plan on taking a bus or a car, keep in mind that most of these vehicules burn fossil fuel. Presently, 7 out of 8 refineries are on strike, with limited consequences. Indeed, the production is not affected and the expeditions to depots and stations are temporary stopped. Authorites states there is no shortage risk. On the other hand, it is said here that the port of Le Havre is completely idle for 3 days, something unseen since 1992. The crude oil supposed to be delivered to refineries is not delivered. You can monitor the potential occurence of an oil shortage there.
Though the french goverment claims that the reform is intended to place everyone on an equal footing, air traffic controller, policemen, customs and a few other jobs got some exceptions, such as still retiring at 52 years old while all the other retires at 62 to 66, getting -10%/+10% of pension. As a consequence, planes operated by non-french companies will likely be flying. While pilots and stewards already saved their own special pension plan, some of their unions are still on strike.
If you want to dodge the risks related to the strikes, you may exchange your ticket or get a full refund on the OUI SNCF website. Otherwise, well... Welcome to France and enjoy Paris!