The method below can be used to convert any accent characters to "?" in a text file. This method can be used to strip accent characters from a subtitle file. The purpose for this is some muxing programs such as dvdauthor will error out when finding these characters.
The method below just converts them to "?". But you can write the results out to a different file then diff against the original to figure out where the characters are then manually convert them if you like.
iconv -f CP437 -t ASCII//TRANSLIT <original file>.srt > <new file>.srt
Then as mentioned you can do this to find where the differences are:
diff <original file>.srt <new file>.srt