Help Identifying Vintage Capacitor Symbol
That's a 10 nF capacitor.  The triangle is not a standard symbol.  It may correspond to a footnote on the schematic.  Or, it is possibly be a voltage range classification, construction type, etc.  If so, that would be listed in the corner of the schematic someplace too.

Just use common sense to determine the voltage and other requirements.  You don't show what is connected to the left of the cap.  The cap may need to be X or Y rated if it touches the power line.  However, since the right side of the diodes are at less than 63 V, this cap probably does not touch the power line.  It is probably being fed from the secondary of a transformer.