How to read NIOS-II General purpose Register specifically r29 (Exception return Address) & r30 (Breakpoint return Address)NIOS-II Processor Reference Handbook Page 3-11
If you are working in C, you may need to create a function in assembly language.See nios2.h and the macros for NIOS2_READ_ET(), NIOS2_WRITE_ET() which operate on register R24 (Exception temporary). I suppose you just need to clone those, but substitute the appropriate register identifier in the assembly language.
GCC generated code will often save r29 on the stack, and then use r29 as a temporary register.Similary the assembler breakpoint stub will save r30 somewhere. So the values in the registers are very boring in any C code.