How to read the value of this capacitor?

0.1uF (100nF) +/-5% tolerance (J), 100VDC rating.

It's a polyester (probably) film capacitor.

Here is a similar type of capacitor (maybe the same type) from Kemet.

Sphero Pefhany already provided the correct answer. Also check the comments below this answer.

The capacitors you mention are NOT using the default capacitor code, which normally is 3 digits for the value followed by one character for the tolerance, and optionally prefixed by a multiplier.

In this link there is a table: Capacitor-Codes

And at the bottom is an additional description (which do not apply your capacitor).