The 2SJ312 is documented in this 362 KB PDF, catalogued as a schematic. Beyond the part number the name says nothing about the equipment involved. The 2SJ code in JIS numbering corresponds to P-channel field-effect transistors, so expect a datasheet with ratings, typical curves and mechanical data. Use it to confirm pin functions while tracing a power switch or driver circuit. Before fitting an alternative, compare drain-source voltage, current, RDS(on) and package to the original.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @cyberlanelectonik. Enginerys does not host this file.
How to open a .pdf file
The standard format for schematics, block diagrams, power-sequence charts and service manuals.