What is the difference between Who watches the World Cup? and Who is watching the world cup? ?Feel free to just provide example sentences.

When we say "Who watches the World Cup?", as an individual question, it implies something like "What kind of person watches the World Cup?". In general, the tone of this could be taken as implying that the World Cup is not something people usually watch. A similar structure could be used for other verbs and other situations. For example:

Who eats pineapple on pizza?
Who works out at 4 in the morning?
Who buys plants for their house and doesn't water them?

In these questions, the implication is that the activity is strange or uncommon, and therefore is difficult to believe or agree with.

When we say "Who is watching the World Cup?", we are asking who is currently, at this moment, participating in the activity of watching the World Cup.
This is a common structure in English, as a present continuous verb tense, in the form of "is ___ing". For example:

He is shopping at the store.
My mother is cooking dinner.
France is playing well in the World Cup.