The statement : There exists a constant $C = C(s)$ such that the continuous embedding of $W^{s,2}$ into the space of uniformly bounded, continuous functions if $s > n/2$, i.e., $$|w(x)| \leqslant C \| w\|_{s,2}$$ for $w \in W^{s,2}$ and almost all $x \in \mathbb R^n$.
I guess $W^{s,2}$ is defined by Fourier transform. In this case, first assuming that w is a test function, we can use inverse Fourier transform. –  Davide Giraudo Sep 28 '12 at 9:09
Strictly speaking, you cannot reduce to the usual theorem, unless $s \in \mathbb{N}$. –  Siminore Sep 28 '12 at 9:26