Part number 2SK2124 is the sole detail here, in a 32 KB PDF catalogued as a schematic and most likely a short datasheet. Under Japanese JIS numbering, 2SK designates an N-channel FET. The maker is not named, so verify it from the body marking. Technicians consult such a sheet for maximum voltage and current, on-resistance, gate charge and package pinout. Those figures decide whether an alternative transistor can safely replace a failed one in a power or switching circuit.
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.