PWM 12V circuit with 300Hz frequency
To generate the signal you need to code it properly. Edit your question if you have specific questions about that but provide a link and page number reference for the section of the datasheet you don't understand.

To measure the signal you have several options:


Oscilloscope.
Frequency meter. Many multimeters have them.
Attenuate to 1 V or so and feed it into the line input of your PC, record it and analyse it with a waveform viewer. Audacity might be good enough.
Attenuate it and play it through some loudspeakers or earphones and check it against a piano. It should be between D and D# below middle C.
Using the above approach check the frequency using a frequency meter, guitar or piano tuner app.