Part datasheet in PDF form for the 2SD966, sized 39.8 KB and labelled with an _E suffix that the name does not clarify. Although stored with schematics, the JIS 2SD prefix identifies an NPN transistor designed for low-frequency circuits. The sheet is handy for checking which lead is which, reading voltage and current limits, and comparing hFE grades. Several manufacturers have produced parts under such numbers, so confirm the package style matches the device on your board.
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.