The 2SK2010 transistor is documented in this 90.1 KB PDF, filed among schematics but in substance a datasheet for an N-channel FET, as the JIS 2SK prefix indicates. It is useful for confirming which pin is gate, drain and source, reading voltage and current ceilings, and judging whether an alternative part will survive in the same circuit. Because the name states nothing beyond the part number, compare the device code and package printed on the component with the drawing before relying on it.
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.