The 2SJ305 is described in this 335 KB PDF, listed among schematics. No board number or brand appears in the name. JIS coding assigns 2SJ to P-channel field-effect transistors, so expect a detailed datasheet with characteristic curves, thermal data and outline dimensions. Repairers use it when a switching or protection stage has failed, checking pin order and limits before testing or replacing the part. Compare ratings carefully and match the package when choosing a substitute.
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.