If $f(x)=x+1$, then write the value of

$f(x)=x+1$

$\Rightarrow(fof)(x)=f(x)+1$

$=(x+1)+1$

$=x+2$

So, $\frac{\mathrm{d}}{\mathrm{dx}}($ fof $)(\mathrm{x})=\frac{\mathrm{d}}{\mathrm{dx}}(\mathrm{x}+2)$

$=1($ Ans $)$