you may find that you need to use a tool from the LHS to remove the freehub. In this case the fastener can be a captive nut or a captive bolt and the threading can be LH or RH. Or the whole thing can screw into the freehub body on a coarse RH thread; there are many variations.
Especially in smaller wheels, it can prove to be virtually impossible to get enough torque to unscrew the freehub body/ fastener. I guess you want to remove it so that you can replace it? In which case you may not know what pattern it is, even, let alone sourced a replacement?
If so, you may find it (net) easier to repair the extant freehub body in situ; they can be rebuilt/reshimmed etc in situ, which completely sidesteps the issue of freehub body removal per se, even if it does raise other issues.
NB in many cases the net result of a repair/reshim is superior to a new freehub body, because new freehub bodies have (or soon develop) free play in the bearings, whereas reshimmed ones are as good as you can be bothered to make them.
It has been my observation that once the bearing surfaces are 'run in' then provided lubrication is attended to, reshimmed freehub bodies can last practically indefinitely. By contrast even if a new freehub has no free play, it soon develops some in most cases.
cheers