On the globe.
I wish this was more obvious, sometimes I have to zoom out and spin the world around to tell.
This isn’t so much a problem on standard missions, where it tells you whether it is day or night. But on special missions I often find myself going in at night when I don’t need to.
On my Steam version, I always see an orange terminator line moving around the globe as hours go by and splitting the more lighted day-time area from the darker night-time ones.
Which you don’t see when your screen is on the night-time/day-time only region, so you
have to zoom out and spin the world around to tell
The world is darker on one side and lighter on the other, I can tell whether it’s day or night easily enough in most situations.
What’s confusing to me is why sometimes I enter a mission and it’s the opposite of what the world map seemed to be - it shows daytime when the line has already crossed to nighttime, or vice-versa. I think the line probably represents midday/midnight, and not daytime/nighttime as I originally thought. If it is, you really don’t have a way of knowing which is it from the globe view.
I can usually tell right away dayside from nightside in the geoscape anyway, as dayside is colored in lighter shades than nightside. But then I’ be never zoomed in from geoscape either.
Anyway, IMO this is not a big deal issue, as a few seconds’ work will give you the info (day va night) you need