Despite how advanced the general ROM hacking and emulation scenes are for the DS then DS 3d ripping is quite primitive compared to many other things you might be coming to use from -- if you were thinking there might be a nice plugin for blender or something that basically does it all like we see on many other systems (amusingly including the 3ds before that all got very advanced) then... not unless you are going to make your own.
Nintendo did provide a format for devs to use, known as NSBMD and related to the BMD formats seen on the gamecube.
However it did not arrive until somewhat into the system lifetime (metroid quite notably uses other formats) so many of the earliest games will not be using it. There are also plenty of games that do they own custom thing, either completely or on top of things.
details the format a bit
has a bit as well.
Tools wise there are two things most care about
1) Textures. Harder as the alpha setups mean even wonder tools like tiledggd which is deliberately built to be incredibly extensible and cover all bases only work for some of the possible texture formats.
In addition to the tile editors for those few things that do anything you are probably going to be looking at tinke for any kind of handling of the oddities, and it is a bit tricky to get going on for general files.
Note also that the DS does not always use textures and instead will often use simple material colours and vertex colours from within the model.
In the early days the main tool was something called nsbmdtool
It was missing things even back then and slowly worked on less and less, I think there is a fork for some pokemon stuff out there as well.
Today most would probably look at apicula
Some emulators might have a limited option but it will be nothing as nice as the 2d side of things.
does some things beyond mario kart these days as well.
3) Animations of various types obviously become the third one but there is very little that handles anything here.
The most common is NSBCA, however there are others that do animations with textures.
I think crystaltile2 might have some very limited support here but it is still going to be worthless as the rest of its 3d handling is not up to much.
The DS 3d hardware is pretty primitive when all is said and done so few things will convert on the fly/leave it as high level formats. To that end any given format will likely play to that.
Any such formats will likely be compressed as well so be prepared to handle that. Most will probably use the main DS formats of LZ compression.
should cover basically all common compressions seen on the DS.
if you need to get hands on and an overview of compressions is needed.
Naturally the gbatek link from earlier will cover compressions as well.
If you are going to edit things then your choices are manual/guided by the viewing tools (nothing stopping you from reloading every time you do an edit/series of edits) + the textures stuff, whatever mkds course modifier can do these days, maybe a few tools for some of the mario games and playing with leaked parts of the SDK. Originally it was an older SDK leak most used here but the gigaleaks saw some new stuff/more complete stuff. In addition to the fun with leaked tools angle then at least the older one required you have what at the time was already an old and hard to come by build of a handful of somewhat offbeat professional 3d modelling tools and this is now many many years on.