As different brands of pressure washer have different types of fittings, any foam cannon / snow foam lance you get will need to have the correct Nilfisk fitting for your model of pressure washer. I don’t think there’s a generic / universal type of fitting that will fit all brands of pressure washer.
As for stone chips - they’re an inevitable consequence of using your car. On a positive note; colour matching white paint shouldn’t be an issue, and once the stone chip has been sorted, if you repair it yourself it’s unlikely to be noticeable to anyone other than you. The cheapest option to fix the one on your bonnet is to get some Seat touch paint from the dealer. I’d advise not applying the paint with the brush inside the cap though - I find these brushes too large, and if you use the supplied brush, you’ll probably end up with an unsightly blob of plaint covering the stone chip. IMO, much better to use something like the end of a cocktail stick or the ends of an unfolded paper clip to get the paint in the chip. The next cheapest option is probably a Chipex or Dr Colourchip paint repair kit. It takes a bit of practice using one of these kits to get a decent result, but there are plenty of YouTube videos showing
how to use them. The beauty of one of these kits is that if you’re not happy with the results, then you can use the blending solution supplied in the kit to remove the paint you’ve applied and start again. The third option - get someone like Chips Away to repair it, but it’s not really cost effective getting them to repair just one stone chip.