When sharpening M390 blade with a coarse whetstone such as 120 or 240 grit size, any type of whetstones will do because at those grit size, you will be sharpening your blade mainly by 'scooping out' chunks of vanadium carbides which are typically around 20 nanometers in size (give or take roughly 50%) embedded in a softer matrix of alloys.
If your M390 knife in question is a typical EDC or bushcraft/hunting knife, then 120/240 grit size will be sufficient. M390 blades. similar to S90V and S110V, perform better when sharpened to low grit size to retain their 'toothiness' for aggressive cutting performance. Kitchen knives such as chef's knife, Nakiri, deba, usuba, etc. on the other hand, require much more refined grinding and polishing work.
As far as I know, there are no mass-production culinary knives made of M390 as of yet. But let's suppose you do happen to have a such knife (maybe you had it custom-made). So as you work your way down to finer grit size, you will have to start abrading those carbides eventually if you want to make further progress at sharpening that blade. FYI, vanadium carbides are approx. 85 HRC on Rockwell C scale, well above the hardness of any traditional Japanese whetstones. So if you attempt to sharpen your M390 blade with a 2000 grit whetstone, the knife will be scraping/sharpening your whetstone instead because those silicon carbides and/or aluminum oxides in whetstones/oilstones are nowhere hard enough to even put a scratch on vanadium carbide.