Hi,
Electrolytic capacitors will have the negative side marked with a "-" sign.
The negative side is the one connected to the aluminum can enclosing it and the positive side is connected through a "rubber" disc.
The 100nF (0.1µF) is a non-polarized component, so in most cases goes in either way - the rare exception is with some foil capacitors, where the pin going to the outer layer is marked, enabling it to be grounded (as shielding) in highly critical circuits handling very low signal amplitudes.