From pictures and schematics on the Digistump site, that's D1 on the Digispark board, which is a 3.6V Zener that clamps the USB D- signal from the ATtiny85 PB3 pin so it doesn't damage the host USB controller. Plugging it in without replacing it would be a *VERY* bad idea. Fit the replacement with the anode to ground. D2 in between the ATtiny85 and the regulator is the same type, so if you can read its markings, you can do a SMD codebook search to find the part number, or trawl through your preferred supplier's parametric search for a small 3.6V Zener with the right dimensions.