Furthermore, your question has multiple answers.
Are you wanting to know where the source for the SIT is stored? If so -- you MUST contact your site support group as there is NO standard place to store the source for these tables -- some sites use a PDS, some use a PDSE, some use CA-LIBRARIAN, or PANVALET, or ENDEVOR, or .... and the data set names will be specific to the site you work for and not likely to be replicated anywhere else.
Are you wanting to know where the compiled SIT is stored? Well, it must be in a library accessible to the region when the JCL is executed. However, this could be a library in the LINKLIST concatenation (hence no STEPLIB or JOBLIB would be needed), or stored in a STEPLIB data set, or stored in a JOBLIB data set. Again, only your site support group can tell you which method is used, and the data set names are specific to the site and may be unique to that site.
So, despite your sarcastic response, the answer "contact your site support group" is the ONLY viable and accurate answer to your question (whatever you really meant by it).