How can I get a list of all misspelled words in a text using Linux?

You can use aspell -a to do this, and take the file from stdout. This will output the word with line number and alternate spellings:

cat example.txt | aspell -a

To clean up your list better, I'd use something more like:

cat aspell.txt | aspell -a | cut -d ' ' -f 2 | grep -v '*'