The 3SK286 is documented in a 22.3 KB PDF listed under schematics, a size and name typical of a short component datasheet. In Japanese JIS numbering, 3SK stands for a four-terminal N-channel field-effect transistor, a class dominated by dual-gate MOSFETs for RF front ends. Technicians check such a sheet for gate and drain pin positions, voltage and current limits and the package type, which matters because small RF devices are easy to fit rotated and damage by static.
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.