First, suspend() is a deprecated method. And it is deprecated because under really rare situations, it was possible to suspend a thread that is owning one of the JVMs internal locks. This will effectively "break" the JVM.
But to answer your question.... You will need to have a collection of Thread objects to search through -- just enumerate through the list to find it. If your application didn't maintain the list, then one option would be to .... (1) start with the current thread, (2) get the thread group and check all the threads own by that thread group, (3) thread groups also own thread groups, so you can also (3a) move up to the parent threadgroup of the current threadgroup and repeat and/or (3b) enumerate the threadgroups own by current threadgroup and repeat (recursively).