。
Want to step outside?
Literal
Surface [to-に] go-out [volitional-ようか].
A tough/confrontational invitation to fight. 表に出る ('go out to the front/outside') is a set expression used figuratively to mean 'step outside (to settle this),' 'let's go somewhere we can fight this out.' 表 literally 'surface, front,' but here it refers to the outside of a building. The volitional ~ようか ('shall we X?' 'want to X?') frames it as an invitation, though the context makes clear it's a challenge. Common in fiction as a line from a character about to throw down. Without context, this sentence is ambiguously friendly; in context, it's combative.