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.

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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? Most of these examples have complements with non-abelian fundamental group. Artin's spinning construction allows you to make knotted spheres in $\mathbb R^4$ from knotted circles in $\mathbb R^3$ -- in particular you can arrange for both knot complements to have the same fundamental group.

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