Exposure questions

Can anyone educate me a bit? I've got two questions:

1) Does exposure stack with debuffs? Would fire exposure stack for instance with debuff from combustion or effect of scorch ailment? I think it should stack, just need the peace of mind :)

2) Is there any way to tell at what stage Scorching Ray is at a given moment? Furthermore do I have to observe the mob's description to know if he's exposed from this particular skill or watch the DOT on the icon not going up anymore? Perhaps there's some visual effect/indication (which stage/max stages?) that I'm unaware of?

Thanks a lot

Generally, only the strongest debuff with the same name can apply to a target, but several different debuffs with the same effect stack without issues.

I do not recall a visual for the stages of Scorching Ray. If you cast it yourself, you would be able to roughly tell from the mana consumption (assuming the mana cost is high enough and your recovery is low enough), but for totems you would need to know the timing.

Yes, exposure will work alongside other debuffs to enemy resists such as the -res on Combustion or curses. Exposure just won't stack with itself through different sources.

Scorching Ray doesn't have a clear indicator of when it's applying exposure. The stages it gains function differently from some other skills, such as Incinerate which shows a "burst" when it hits max stages, in that the stages aren't applied to the skill itself. Instead, they are applied to the individual mobs as they remain in the beam. If a mob hasn't been in the beam for a full 8 stages, it's not getting fire exposure applied to it.

The best you can do is keep an eye on the mob stats so you can see if/when it becomes vulnerable to fire. It also helps a lot to calculate your cast time to hit 8 stages. Then you'll at least know how long you need to channel on each mob to apply exposure to them.

PoE is just incredibly poor at giving visible cues or feedback on some of these kinds of things.