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?