What type and size capacitor goes on a Baldor 1/3 HP bench grinder

Much would depend on whether it is a start capacitor or a start/run capacitor.
If there is a switch on the end of the rotor operated by centrifugal weights it will be a start capacitor only but if there is no centrifugal switch the capacitor will need to do double-duty and the value could be critical.

Contacting a dealer or the manufacturer would be favourite but a motor specialist might be able to make a recommendation. Guessing isn't really an option and the working voltage of the capacitor is equally important. Most generic capacitors are rated in dc volts and for them to be safe used on ac mains the working voltage must be considerably higher than the rms value of the ac mains. It is best to use only capacitors rated for ac mains.

You will probably find the capacitor as a spare part from a dealer will be prohibitively expensive but once the value has been discovered and if possible the manufacturer, part number and so forth, great savings can be made by sourcing direct from the capacitor manufacturer.

I recently paid less than £5 plus carriage plus VAT for a capacitor the machine manufacturer wanted more then £60 for.
Good luck!