They are not the same.
The correct form would be:
- He knows his girl's gonna talk about it all day.
- He knows his girl is gonna talk about it all day.
When there is evidence that something is likely to happen (in the future), you might want to use this form:
to be + going to = to be + gonna
"Gonna" always has to be followed by an infinitive. It can only be used in spoken form, both formal and informal.
In written form (also in spoken language) it will be:
- He knows his girl is going to talk about it all day.
In you last sentence you've used the word "gone", perhaps accidentally, because that means "no longer present". So it can't be used in this sentence.
I hoped this helps.