The short answer is : You better not.
The long answer is :
You can duplicate the dataset Louis talked about and add the informations of the second Catalog environnment.
BUT, you will have to find a way to differentiate in your processes where the initial call originates from.
I may suggest to use a different user for each environnment and validate it in your process.
switch(Process.callerUser)
{
case "userA" :
Process.myDataset = Datasets["PAM/Library/CA SLCM/SLCM_GlobalDatasetA"];
break;
case "userB" :
Process.myDataset = Datasets["PAM/Library/CA SLCM/SLCM_GlobalDatasetB"];
break;
default :
Process.myDataset = Datasets["PAM/Library/CA SLCM/SLCM_GlobalDatasetA"];
}
The true advice here is : Do not go there. It is way less effort to have separated environnement. If it is training and dev setup and you have financial limitation, you can install a complete EEM, Catalog and PAM environnment on a single box. Just pay attention to port issues.