If the LC+ 2.0 is the same as my 2009 LionMaster, and I believe it is, there is one smoke unit and it doesn't matter which hole you pour the smoke fluid in. I would say start with 20 drops to avoid possibly over filling the smoke unit and having smoke fluid leak all over you new locomotive! How exciting, new Big Boy on your layout.
Thank you WesternPacific2217, now that I have it unboxed it appears it does not matter which hole it goes in. It appears the fluid just travels to the center between them. It did come with a funnel which surprised me because it doesn't seem to be a tight spot to get fluid. Maybe the funnel is to allow the fluid to be put as close to the center of both holes as possible? It is very nice looking. Everything looks great out of the box. Seems lubed well and no loose or broken parts. Will get it on the track soon.