This paper serves two purposes, by adopting the classical Casselman–Tadi
c
´
\acute {c}
’s Jacquet module machine and the profound Langlands–Shahidi theory, we first determine the explicit Langlands classification for quasi-split groups
P
G
S
O
8
E
PGSO^E_8
which provides a concrete example to guess the internal structures of parabolic inductions. Based on the classification, we further sort out the unitary dual of
P
G
S
O
8
E
PGSO^E_8
and compute the Aubert duality which could shed light on the final answer of Arthur’s conjecture for
P
G
S
O
8
E
PGSO_8^E
. As an essential input to obtain a complete unitary dual, we also need to determine the local poles of triple product L-functions which is done in the appendix. As a byproduct of the explicit unitary dual, we verified Clozel’s finiteness conjecture of special exponents and Bernstein’s unitarity conjecture concerning AZSS duality for
P
G
S
O
8
E
PGSO_8^E
.