PSX VRAM is a 1MB 1024x512 raw image at BGR555 (16 bit). You can just dump the VRAM with pSX and then view it with psxvram by agemo or tile molester. The right-hand side of the VRAM is used to store textures to be loaded in the screen buffer on the left. Such textures can be either in 4bpp or 8bbp format, so you should change encoding for a correct visualization. At the bottom left side you can see the palettes of every 4bpp/8bpp texture stored on the right side. Such palettes are in BGR555 format too.
To get the offset of a particular coordinate in VRAM, let's say x,y, it is just y*2048 +x*2 (2 bytes per pixel, 1024 pixels per row). Note that PSX does not store images by tiles.