For a satellite I know the period T and frequency f = 1/T. For instance, for an earth skimming satellite with period T = 5100 seconds, the frequency is f = 0.00019 1/sec. What does the number 0.00019 represent? Is it the angle in radian per second?
And how do I visualize the wavelength of the satellite's orbit?
If the satellite has a period of $T$ seconds (so it makes one complete revolution in this time), then its frequency of revolution $\frac{1}{T}\ s^{-1}$ represents the number of revolutions it makes per second (assuming circular orbit). So if $T=5100\ s$ then the satellite makes $0.00019$ revolutions per second, or $f=0.00019\ s^{-1}$.
If you wanted to determine the angular frequency, or the frequency in radians per second, then you would calculate $$\omega=\frac{2\pi}{T}=2\pi f\approx 0.0012\ \text{radians}\ s^{-1}$$
You might think that since an object has a frequency, then it should have a wavelength. But here, frequency or angular frequency are terms associated with the speed or velocity of the object. E.g., angular frequency being the magnitude of its angular velocity, which is a (pseudo) vector. In this particular case, physically the object does not possess a wavelength. Wavelengths are associated with waves, so in the context of your question, we don't really attribute a wavelength to such a situation.
