// Assume MethodGen mainMG is given to us
Instruction[] insns = mainMG.getInstructionList().getInstructions();
for(Instruction insn : insns) {
    if(insn instanceof InvokeInstruction) {
        // great, found an invoke instruction
        InvokeInstruction invoke = (InvokeInstruction)insn;

        // what do I do with it now?
    }
}