Translation:He has the better jacket at the club.
he has the better jacket in the club - this sentence in english sounds strange
It even sounds odd in german, don't worry. It's just a bad, uncommon, example.
This makes sense me only if he owns two jackets and has left the better one at the club. Like, he's leaving home and puts on the lesser jacket, leaving someone to explain "He has the better one at the club (as in, not here)."
If you had the context, I'd concede 'the better jacket', but when you're faced with the sentence in isolation pretty much every English would think 'the best'.
Because it sort of leads to "They Won the world cup, they are the better team in the world"
In English, this is only grammatically correct if there are two jackets in the club. Otherwise you must use "best." Is German different or the same? Does "bessere Jacke im Verein" imply there are only two jackets in the club, and if 3+ then "beste"?
in some contexts, it sounds OK. e.g. the club has two jackets of different quality. he has the better jacket.
"at the club" only makes sense if you're talking about a building that is a club. Verein is a club/organization, not club/bar/dance hall.
these cases of 'the better thing' are just ODD. there is no context at all that allows us to know that they are not superlatives, but rather comparisons.
i guess his jacket is particularly impressive at the club, and not so great elsewhere
"im" is a contraction of "in dem" right? So if instead of Verein you said Wohnung, the sentence would be "Er hat die bessere Jacke (in der?- ir?) Wohnung.