You can use m6811-elf-readelf or m6811-elf-objdump to look at the content of any object file.
To disassemble the file, you can use the following command
m6811-elf-objdump -d file.o
And if you have compiled your program with debugging information
(-g or --gdwarf2) you can disassemble and show the
source code with the following command:
m6811-elf-objdump -S file.o