Why is it "det" when tidning as an n-word?
"det är" is always "det är" regardless of gender. It's a little blessing. I believe it mentions this in the Tips and Notes section.
How do you know when to use ett tidning or en tidning??
You don’t. You have to learn the gender for every word. However, words on -ning are usually en.
''Det'' is pronounced ''dyet''?
No? Sounds OK to me...
Is 't' in det not pronounced,