Since $f(a)=2$,

We have $f(a)=a^{3}+\\sin a+1=2$, which simplifies to $a^{3}+\\sin a=1$,

Also, $f(-a)=(-a)^{3}+\\sin (-a)+1=-(a^{3}+\\sin a)+1=-1+1=0$.

Hence, the answer is $\boxed{0}$.

By substituting $α$ and $-α$ into the function respectively, we can obtain $f(a)=a^{3}+\\sin a+1=2$ and $f(-a)=(-a)^{3}+\\sin (-a)+1$. By analyzing the relationship between them, we can derive the answer.

This question primarily tests the application of function's odd and even properties. It is a basic question. The key to solving it is to observe and analyze that the part $x^{3}+\\sin x$ is an odd function.