(Very) partial answer
The message (which may just be the beginning of the puzzle) is:
Did you notice the __o_i__
But I can't find any dictionary word that satisfies the final paragraph as it stands...
The first is in cod but not anchovy
The second is in fire and also in inferno
F, I, R, or E
The third is in aikido but not in jujitsu
A, K, D, or O
The fourth is in hey and also in hiya
H or Y
The fifth is in navigator but not in traveller
N, I, G or O
The sixth is in obtuse and also acute
U or E
The seventh is in optician but not in optic
A or N
The eighth is in song and also in carol
The ninth is in entrance but not in amaze
N, T, R, or C
The tenth is in email and also listserv
E, I, or L
The eleventh is in car but not in axle
C or R
The twelfth is in cider and also in beer
E or R
The thirteenth is in star-roof but not in moonroof
S, T or A
The fourteenth is in ham and also chorizo
The fifteenth is in gel but not agar
E or L
The sixteenth is in cloudy and also in clear
C or L
The seventeenth is in terrier and not in corgi
T or E
The eighteenth is in hot and also in cold
The nineteenth is in elastic but not in band
E, L, S, T, I, or C
The twentieth is in tin and also in foil
The twenty-first is in neglect but not in abuse
N, G, L, C, or T
The twenty-second is in Macgyver and also in Angus
A or G
It's pretty easy to find grammatical English words to match the first four paragraphs, but that leaves us with the last paragraph:
DID YOU NOTICE THE [C,L][T,E]O[E,L,S,T,I,C]I[N,G,L,C,T][A,G]
and I cannot get any sense out of it. Perhaps it is:
Anagrammed or otherwise encoded, which makes the puzzle more difficult...
Among the things I've tried:
Adding a missed word break: The only words I can make with this are DID YOU NOTICE THE CEO SING (which sounds like a weird question).
Reversing the positions of the two words in each of these 7 lines (makes [C,L][C,O,G]O[B,N,D]I[A,B,U,S][A,G] for the last word which gives no dictionary words).
Making each of the comparisons wrong (in becomes not in and vice versa): makes [O,U,D,Y][R,I][H,T]A[T,N]E[M,C,Y,V,E,R] for the last word which gives no dictionary words.
Making one of the comparisons wrong (in becomes not in and vice versa): also makes no dictionary words
I'm guessing that:
The thing I need to notice is a seven letter word describing what has been done to the final paragraph
@Postmortes has noticed that:
The last letters of each line spell out YOU ARE CLEVER FOR RIDDLES which makes some sense but is ungrammatical... I can't see where to go from here yet.
Also, if we look at which lines:
Have 'in' before the last word and which do not, we get the binary sequence $0111101110111001111111$; I don't know if that is relevant.
I've also tried:
Looking at what connects the comparison words in each line to see if that gives us a meaningful string of words, but can't get anything meaningful out of that - in fact for some of the words it's hard to find a class to which they both belong, as they are more loosely semantically related (e.g. navigator & traveller, optician & optic, email & listserv). Some (like entrance & amaze) have an even more tenuous link (unless amaze is a play on 'a maze').