Datasheet PDF for the 2SD1222, sized 183 KB and placed in the schematic section of the index. The part follows the JIS scheme, where 2SD denotes an NPN transistor for low-frequency work; the name adds no package or variant detail. Sheets like this present voltage and current limits, power dissipation, gain groups and lead order. Technicians use the data to test the transistor, mark its pins correctly on the board and verify that any equivalent offers comparable gain and equal or higher ratings.
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.