What does probably mean?

: insofar as seems reasonably true, factual, or to be expected : without much doubt is probably happy it will probably rain.

How do you say spell probably?

Probably, probably. As I said, some people will reduce this to two syllables, so you might here pro-bly, -bly, without the middle syllable. Prob-ly, prob-ly.

How is 2020 pronounced?

You’d say: twenty twenty. The second is to say: two thousand and twenty.