The word "on"
Please, can anyone explain the grammatical function of the word "on" in these sentences? Can the word "on" be omitted or have meaning?
Thank you very much.

What´s on?
What time is it on?
It’s on at 12 o’clock
It is on evening?

Question

The word "on"
Please, can anyone explain the grammatical function of the word "on" in these sentences? Can the word "on" be omitted or have meaning?
Thank you very much.

What´s on? 
What time is it on?
It’s on at 12 o’clock
It is on evening?

Answer

I'm assuming Question 4 is supposed to read 'Is it on in the evening?' - or if it's a statement, 'It is on in the evening.'

Answer

The first three sentences seem to be asking about TV or radio shows.  We say that programs are "on" electronic things like the TV, the radio, or the internet, while news is "in" printed things like newspapers, magazines, and books.

Therefore, the questions are as follows:
1. What (show) is on (the TV/radio right now)?
2. What time (does) it (come) on (the radio/TV)?
3. It (comes) on (the TV/radio) at 12 o'clock.

Question 4 is nonsense, and has no discernible meaning whatsoever.

Ne manquez pas cette occasion d'apprendre une langue depuis chez vous. Découvrez notre sélection de professeurs de langues expérimentés et inscrivez-vous dès maintenant à votre premier cours !