よくね? = よくない? = "Isn't it nice?"
As for this particular word form, it is a relatively recent slang in casual speech. This ね was developed from ~ない? which functions as tag question "isn't it?", thus always carries a mild to acute uptalk intonation, whether or not written with a question mark.
Its grammatical construction follows the etymology. That is, [noun/na-adj] + じゃね?
, [i-adj] + くね?
, and [verb]-未然(nai-stem) + ね?
(in which case means "why don't —?").
The most remarkable feature of this expression which is not predictable from its origin is the completely flattened phrasal accent.
いいんじゃね{LHHHHH}? vs いいんじゃない{HLLLLLL}?
やばくね{LHHH}? vs やばくない{LHLLL}?
かえらね{LHHH}? vs かえらない{LHHLL}?
(the effect of question intonation is excluded; all examples have a rise in the last syllable)
This effectively yields a straightly upward phonetic realization, very much close to that of an English yes-no question sentence.