Hello!

My opponent controls a Doubling Season. I've exiled his Jace, The Mind Sculptor with my Banishing Light.
If my opponent breaks my Banishing Light, his Jace will enter onto the battlefiled with twice its loyalty counters or not?

I've problems in understanding if the one-shot effect created when Banishing Light leaves the battlefield can be considered an “effect” according to CR 609.1 and, consequently, Doubling Season can apply to it.

Thanks!

Yes, the one-shot effect created when Banishing Light leaves the battlefield is an effect. Doubling Season will apply to it, so Jace, the Mind Sculptor will enter the battlefield with double his usual complement of loyalty counters.