I took a new programming job six months ago.  The company is growing fast and our group has been very busy.  My manager is happy with my work but she recently hired another manager for our group who isn't that good. I've told my manager I would quit if I had to report to him.Anyways I got an email from Pager Duty saying I'm "going on call" soon for a part of the system I've never worked with.  I'm not an SRE and I didn't agree to be on call when I joined this company. 
The new manager added me to his on call list for a system I know nothing about.I'd feel different about it if this was something I worked on but thinking about this is stressing me out.  I don't know the best way to proceed.  I'm tempted to ignore it completely but I know this will come up.I don't want to have to quit but I don't want this new guy thinking he can sign me up as an SRE along with his other reports.Anyone have any suggestions?