I have a hemlock rustic dining room table with a semi gloss finish. I recently tried to buff a smudged area with 0000 steel wool and paste wax. It left a haze with surface scratches on the finish. How do I fix this?
You've scratched the finish and you need to polish/buff out the scratches.
Before we begin I'll be upfront with you here, because your table has a semi-gloss finish it may be very difficult indeed to buff out an area and have it exactly match the sheen of the surrounding varnish.
Buffing out varnish can be done using a number of polishing agents (see previous Answer). But before you go and get a product to try to repair the finish you may actually get some traction using a couple of things you probably have in the house already.
Possible quick-and-dirty fix
Just by buffing with some cloth (e.g. denim) or even brown paper (!) could be enough here. For the denim or a paper bag the inside surface is usually the one to go with, slightly rougher in both cases.
There's no downside to trying either or both of these first since they won't further harm the varnish. If you don't get quite the result you're looking for you can move up to a commercial polishing agent.
I would try the brown paper first, working gently at first and then increasing pressure. If it's still a bit hazy move to the denim. Buff firmly with this, you can usually raise a pretty decent shine on varnish with denim and some elbow grease.
What to do if the area remains clearly visible
This is going to seem radical but you might consider using your 0000 steel wool and paste wax to work the entire table surface. Finish with long strokes following the grain, trying to go the full length of the table if possible.
Once the surface is all scuffed to a consistent light haze you can then decide how to proceed. It is much easier to work all of a surface to a uniform sheen than to try to do one spot and get it to seamlessly match what's around it (unless the surface is a full-on gloss).
But you might actually discover than once scuffed uniformly that you can live with the table as it stands — many pros actually get a satin surface by scuffing up gloss poly using steel wool so this is a widely accepted finish.