Answer
$\not \subseteq$
Work Step by Step
$A \subset B$ if all elements of set A are also elements of set B.
Note that an element of the set on the left ($8$) is not an element of the set on the right. This means that the set on the left is NOT a subset of the set on the right.
Thus, the missing expression in the given statement is $\not \subseteq$.
