  One of the most important and actual issues in relativistic astrophysics is
testing gravity theories and obtaining constraint values for the parameters of
black holes using observational data. In this research, we aimed to explore the
optical features of a Kerr--Newman black hole model in the presence of a
quintessential field, which may be a candidate for a dark-energy model with a
nonzero cosmological constant. First, we obtain the equations of motion for
photons using the Hamilton--Jacobi formalism. We also study the horizons and
shapes of the apparent regions of the photon region around the said black hole.
In various scenarios, we investigate shadows cast by the black hole using
celestial coordinates. Furthermore, we analyze the effects of the
quintessential field and black hole charge on the shadow radius and distortion.
Furthermore, we look into the constraints on the spin and charge of
supermassive black holes M87$^*$ and Sagittarius A$^*$ for different values of
the quintessential field using their shadow size measured by the Event Horizon
Telescope Collaboration. Finally, we study the effects of the quintessential
field, black hole spin and charge on its energy emission rate by Hawking
radiation and compare our results with those of the available literature.
