Unfortunately, it's in the core files. You'll want to find the snippet you want to change, then search the lang files for it. Most text on the site is stored in a lang file.
For instance, if you want to change "Your comments or suggestions..." it's here:
qa-include > qa-lang-misc.php > line 52
The other text snippets for the feedback form are also in there:
'feedback_email' => 'Your email: (optional)',
'feedback_empty' => 'Please use this field to send some comments or suggestions',
'feedback_message' => 'Your comments or suggestions for ^:',
'feedback_name' => 'Your name: (optional)',
'feedback_sent' => 'Your message below was sent - thank you.',
'feedback_title' => 'Send feedback',
You'll want to change the words after ...=> ' and before ...',