The 2SK1891 transistor is covered by this 96.0 KB PDF, which the index lists as a schematic. A 2SK prefix is the Japanese designation for an N-channel field-effect transistor, so the document is most likely its datasheet. Use it to confirm gate, drain and source pins, check drain-source voltage and current limits, and note the package when hunting for a replacement. Beyond the part number the name carries nothing, so match the device marking against the document.
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.