  We consider Klein-Gordon equation in the Dyonic Kerr-Sen black hole
background, which is the charged rotating axially symmetric solution of the
Einstein-Maxwell-Dilaton-Axion theory of gravity. The black hole incorporates
electric, magnetic, dilatonic and axionic charges and is constructed in 3+1
dimensional spacetime. We begin our investigations with the construction of the
scalar field's governing equation, i.e., the covariant Klein-Gordon equation.
With the help of the ansatz of separation of variables, we successfully
separate the polar part, and find the exact solution in terms of Spheroidal
Harmonics, while the radial exact solution is obtained in terms of the
Confluent Heun function. The quantization of the quasibound state is done by
applying the polynomial condition of the Confluent Heun function that gives
rise to discrete complex-valued energy levels for massive scalar fields. The
real part is the scalar field relativistic quantized energy, while the
imaginary part represents the quasibound states's decay. We present all of the
sixteen possible exact energy solutions for both massive and massless scalars.
We also present the investigation the Hawking radiation of the Dyonic Kerr-Sen
black hole's apparent horizon, via the Sigurd-Sannan method by making use of
the obtained exact scalar wave functions. The radiation distribution function,
and the Hawking temperature are successfully obtained.
