The three words that actually combine two suffixes and are written correctly are:
Fearlessness
Hopelessness
Effortlessness
What is suffix?
Suffixes are known to be an affixes that are added to the end of a word to form a new word. They actually form a new word with a different meaning.
We can see that such words that combine two suffixes and are written correctly are: fearlessness, hopelessness and effortlessness.