I'm looking for extensions of the quadratic closure of $\mathbb{Q}$ of
degree $3$,
degree $5$.
Furthermore,
Does there exist an extension of degree $4$?
What I know:
I know that the quadratic closure of $\mathbb{Q}$ in $\overline{\mathbb{Q}}$ is
$$Q^q:=\bigcup_{i=0}^\infty \mathbb{Q}_i,$$
where $\mathbb{Q}_0=\mathbb{Q}$, and $\mathbb{Q}_i=\mathbb{Q}_{i-1}(\sqrt{\mathbb{Q}_{i-1}})$.
However I wouldn't know how to find extensions hereof, especially when they're of a certain degree.
For the second question, I would say, intuitively, that the answer is no. But again I'm not sure why.
The question of whether $\Bbb Q^q$ has any extensions of degree $4$ is very interesting. It does, for:
Let $\rho$ be quartic over $\Bbb Q$ with its splitting field $K$ having $S_4$ as Galois group (over $\Bbb Q$). So $[K\colon \Bbb Q]=24$. This $K$ is the normal closure of $\Bbb Q(\rho)$, that is, it’s the intersection of all normal extensions of $\Bbb Q$ that contain $\rho$. In other words, every normal extension $\Omega$ of $\Bbb Q$ that contains $\rho$ must satisfy $K\subset\Omega$. Since $K\not\subset\Bbb Q^q$ (again, by degree considerations), we see that $\rho\notin\Bbb Q^q$.
Now I claim that $\rho$ is still quartic over $\Bbb Q^q$. Let $f$ be the $\Bbb Q$-minimal polynomial for $\rho$. Over $\Bbb Q^q$, $f$ will have no roots, thus will either split into a product of two quadratics, or remain irreducible. If product of two quadratics, the roots of one factor of $f$ will be quadratic over $\Bbb Q^q$, so in that field. Only remains that $f$ is irreducible over $\Bbb Q^q$, in other words $[\Bbb Q^q(\rho):\Bbb Q^q]=4$.