Or maybe it shouldn't, in general, vote at all on that as a separate question (after first resolving if people really want to go forward with the current exit process now that there is more clarity on what that entails) except perhaps to confirm it reject an exit under a deal negotiated after a government-decided invocation of Art. 50 provides a concrete choice, since it's a complex question involving potential for negotiated terms that intersects with every other policy area; maybe the UK should vote for a Parliament and let Parliament balance the issues, proposing referenda only when the public have he information about the choices that makes the decision meaningful.
The first referendum on Brexit was a fairly naked political ploy to punt on exactly that Parliamentary duty with the hope of creating partisan advantage in a general election.