MJP files are "Masked JPEG" files, they are custom to the C3 engine (i.e. TQ Digital games) and are basically used on mobile games instead of DDS or PVR formats to leverage the built-in hardware decoders for JPEG. They are texture files. As JPEG does not support transparency, there is a mask to emulate it. Here is a decoder written in Rust:
For DMap files, you'll find implementations in most public sources of Conquer Online, or in the leaked Soul project if you can find it. There are not really any public editors, and the best you can get as a utility for DMap files is this: