Strikes just have been confirmed for 29 and 30 November, and the 1st of December in Belgium.
The 29th will be the most heavy strike, with all unions having confirmed to participate. Traffic will be heavily interrupted from monday 28th of November 22:00 h.
The 30th and the 1st only one union is going on strike. This one has quite a strong foothold in Wallonia (Southern, French speaking part of Belgium). Northern part should be relatively okay service-wise 30 nov and 1 dec.
An alternative service will be in place every of those day. You can check one or two days before the strike which trains will be available via: https://www.belgiantrain.be/en/travel-info/train-network-travel-info/strike (domestic traffic) and https://www.b-europe.com/EN (for international traffic).
For the moment they expect that most international traffic will run (Thalys, Eurostar, TGV, IC Amsterdam-Brussel, no news on the ICE or Nightjet yet), but you might have troubles finding connections to other parts of Belgium.