But there are non-trivial torus knots in $\mathbb R^4$. The simplest examples are achieved by attaching a handle to a knotted $S^2$ in $\mathbb R^4$.  How do we know they're knotted? The simplest examples have complements with non-abelian fundamental group.  Do a google search for "2-knot" for examples.  

Or did you mean to add additional qualifiers to your question?