Let $(J,\pi)$ be a cuspidal type in $SL(2,F)$, $F$ is a nonArch. local field and let $I$ be the Iwahori subgroup of $SL(2,F)$.
Is there any possibility that $J\subset I$ or even a subgroup?
Let $(J,\pi)$ be a cuspidal type in $SL(2,F)$, $F$ is a nonArch. local field and let $I$ be the Iwahori subgroup of $SL(2,F)$. Is there any possibility that $J\subset I$ or even a subgroup? 


Here is a novel, explicit answer to your question : Benedict Gross and Mark Reeder have recently discovered a family of supercuspidal representations, called "simple supercuspidal representations", of simply connected, split, almost simple, reductive groups. These representations are examples of what you are looking for. Here's an example of a simple supercuspidal representation, and the general case is similar. Consider $G(\mathbb{Q}_2) = SL(2,\mathbb{Q}_2)$. Let $I$ be an Iwahori subgroup of $SL(2,\mathbb{Q}_2)$, and let $I^+$ be the prounipotent radical of $I$. For example, we can take $$I = \begin{bmatrix} \mathfrak{o} & \mathfrak{o}\\\ \mathfrak{p} & \mathfrak{o} \end{bmatrix}$$ $$I^+ = \begin{bmatrix} 1 + \mathfrak{p} & \mathfrak{o}\\\ \mathfrak{p} & 1 + \mathfrak{p} \end{bmatrix}$$ Let $\chi$ be an "affine generic character" of $I^+$. Since we are dealing with $SL(2,\mathbb{Q}_2)$, this just means the following : Let $\eta$ be the character of $\mathbb{Z}_2$ given by $$\eta : \mathbb{Z}_2 \rightarrow \mathbb{C}^*$$ $$2 \mathbb{Z}_2 \mapsto 1$$ $$1 + 2 \mathbb{Z}_2 \mapsto 1$$ Then define the character $$\chi : I^+ \rightarrow \mathbb{C}^*$$ $$\begin{bmatrix} a & b\\\ 2c & d \end{bmatrix} \mapsto \eta(b) \eta(c)$$ Then $Ind_{I^+}^{SL(2,\mathbb{Q}_2)} \chi$ is a supercuspidal representation (which Gross and Reeder call a "simple supercuspidal representation", since it is so "simple" to define). The general situation is similar : If $G$ is simply connected, split, almost simple, $F$ is a $p$adic field, $I \subset G(F)$ is an Iwahori subgroup, $I^+ \subset I$ is the prounipotent radical, and $\chi : Z I^+ \rightarrow \mathbb{C}^*$ is an "affine generic character" (where $Z$ is the center of $G(F)$), then $Ind_{Z I^+}^{G(F)} \chi$ is a supercuspidal representation (called a "simple supercuspidal representation"). For more details, check out Section 9 of https://www2.bc.edu/~reederma/AdjointGamma.pdf 


Yes this is indeed possible. You may read the proof of theorem (2.1.) of Bushnell and Kutzko, The admissible dual of ${\rm SL}(N)$  I Ann. Sci. École Norm. Sup. (4) 26 (1993), no. 2, where the supercuspidal representation are described as induced representations from a subgroup wich can always be taken of the form $U({\mathfrak A })\cap {\rm SL}(N)$, where $\mathfrak A$ is a principal order in ${\rm M}(N,F)$. But of course, you may replace the group $J$ by a maximal compact subgroup by inducing the type to a maximal compact subgroup $K$ containing $J$. 


While possible it only can happen if the quadratic extension associated to the type is ramified. 


The Iwahori is a type for the trivial representation on the Levi for $SL_2(F)$. Moreover all the types for $SL_2(F)$ of non supercuspidal bernstein components are subgroups of the Iwahori. There is a paper by Kutzko where he describes all the types for $SL_2(F)$. 

