'sina tawa sitelen tawa, anu seme?' Are you going to the movies or what?”Legitimate answers include: '(mi)tawa (sitelen tawa), “(Yes, I'm} going” ; '(ala. mi tawa) tomo moku. “(No. I'm going to) the diner”; '(ala. mi) awen lon tomo' “(No, I'm) staying home”; and '(ala.) jan meli li kama tawa tomo mi.' “(No) a woman is coming to my place.” A simple 'ala' “No” seems inadequate or inappropriate, not among the choices offered (except for the Tweedle threat “You will come or else.” “Or else what?” “Or else you won't, of course”).
All of which raises the question of just what is the grammar of 'anu seme', what is 'seme' disjoined with? The answer seems to be with predicate or object or even the whole sentence and, so, “the whole sentence” seems to be the best answer, since the reduction to a part is familiar in context. So, 'seme' here is a prosentence.
And that answers the question of how to punctuate two sentences joined by 'anu', of which we have so few (no?) examples. Since a fairly common occurrence (though not an official one) is that the question is punctuated as above, with a comma before 'anu', and this makes good sense syntactically (distinguishing from alternation – in this case – with the object or the predicate), let's assume that the best style is 'S, anu S', whether this is for a question, “Are you going to the moving or is Molly coming over” 'sina tawa sitelen tawa, anu jan Mali li kama?, or statement, “You go to the movies or Molly comes over” 'sina tawa sitelen tawa , anu jan Mali li kama' .
But what about compound sentences with 'anu'. The analogy with 'en' suggests that in NPs 'anu' just goes between the two pieces (with an added 'pi' when the pieces are modifiers) and the same presumably applies for PPs. But what about predicates and DOs, which do not use 'en' for “and” compounding? In simple cases, verbs without direct objects or DOs without following PPs, we could easily just join the two conjoined expressions with 'anu', creating no more problems than a similar approach does in subjects. But DOs subsume the following PPs and verbs the following DO+PPs and modals everything following.
First thoughts on this, thinking mainly about minimizing ambiguities, suggest that, when PPs are involved, the 'e' for compounded DOs should be used: 'e ijo, tan ilo anu e ilo, tawa ijo', which, if PPs are retained, the 'anu' can just joint the NPs: 'ilo anu ijo, tan jan'. Similar reasoning seems to apply for predicates and 'li', given DOs or PPs. There remains the possibility that a DO or PP that goes with the second predicate (or DO, for that matter) might be taken as going with both, but that seems well within the usual range of ambiguities in tp, whereas the complexities surrounding compounding do not. The case of compounding predicates after a modal, if there are any flourishes, don't seem to have a clear solution – either way starts a new set of problems.
Of course, the toki pona solution to all of this is “don't compound sentences on predicates or DOs – and probably not elsewhere either if you can help it.” Better advice than all the grammatical jiggery-pokery.