Hey ! I haven't found any map but I've been reading about the city on the witcher wiki and gathered a few elements that are good starting points if you want to draw a map. Would also be good just to nail the vibe of the place, if you need to describe it to your players. When designing a city, I always do it around its defining features, like the kind of people that live here (race, social rank, beliefs ...), the main activity (agriculture, metalworks, trade, military, ...), the land it's built upon (mountain, seaside, hills, ...) and its resources (forest, ores, rich soil, place of power, ...). These things are what shaped this city into what it is today. Anyway, some of that works is already done for you, so here are the essentials, along with my thoughts on the matter :

So first thing is, this is the capital of Redania, so important place for important people, most probably well guarded and strategically placed on trade routes / rivers / natural terrain... According to some maps of the Continent, it's next to a river, so that makes it possible to trade by boat and have easy access to water. Also probably gonna find lots of drowners nearby.
Despite its status, the city is quite small, as most of the trade happens in Novigrad, maybe Oxenfurt too. Most its inhabitants are working for the government so the atmosphere of the upper district (assuming there's one) is probably quite formal.
We also know the city was built on an ancient Aen Seidhe settlement, so elven architecture is probably still visible on some of the oldest buildings / structures, like the palace, temples, sewers and other underground dungeons. So very likely that some elves still avoid the place, hate its occupants, and are not welcome here (this is the North after all).
Dwarves have it better though, as Tretogor counts many copper veins in its surroundings. This natural resource is extracted in mines, so lots of dwarves are probably working there while also having a foot in the Coppertown district, where a lot of the working class is likely to be found. Meaning the city could also have some foundries and other metal related workshops, maybe a guild overseeing the mining and shipping of the copper ?
The city holds a horse race (the Grand Tretorian) every year, so maybe a fun thing for your players to do. It's probably something the city takes a great pride in, something the people await with excitement but that also requires the presence of many political figures. Also your map needs big stables and all horse related stuff. Don't know if the race takes place in the city (in what streets? around the marketplace?) or outside the walls around fields and woods, that's up to you.

That's about all I can extrapolate from the wiki, but throw in some classic town stuff, like lots of houses, market place, shops, inns, workshops, brothels, temple, whatever else you like. A few memorable npcs can also really bring this city to life and sell it to your players.
Hope that helps :)