There are anagrams of stone in every line except the fourth and fifth: (tones), (notes), (set, no), (onset). An anagram of stone also appears in the title: (Ten So).
In addition, stone is hidden forwards in the fifth line (last on every) and backwards on the fourth line (me not? Scan).
the poem fits the answer, even if it doesn't unambiguously define it. The first three lines are quite clear. The "Scan carefully" could be interpreted as leaving no stone unturned: the anagrams can be "turned" to get "stone".
With 6 I thought it was 6 times "No" was repeated. Also, "From first to last on every row." I guess the letter which are present in each line which gives "onset" which are present on every line which when anagram gives english words like "notes", "stone" and very importantly "Steno" who is a shorthand typist.
I am really horrible at steganography But here is what I found out so far.
There are 10 capital letters in the text. 10 in total, and 6 before the "?" which could be a clue related with the title.(or just pure coincidence.)
The riddle tag was explained as being debatable which means it's really just the result of steganography. But since the tag was still added it means that among the riddle, there is probably a clue to how to solve the steganography problem. Which makes me think that the last 2 rows are a clue as to how we must do something with the beginning and end of each lines to find the solution.
I also noticed that a dot was omitted after "Scan carefully" which is probably an important detail.(or a typo)