I’m what stage of cellular respiration is most of the carbon dioxide produced?

The “light cycle” or Krebs.

The Krebs cycle or the TCA cycle produces
2
C
O
2
for every
1 molecule of acetyl CoA
.
This occurs in Step 3 and Step 4 of the Krebs cycle.
In Step 3,
isocitrate
is oxidized to become
alpha-ketoglutarate
by the rate-limiting enzyme,
isocitrate dehydrogenase
.
In Step 4,
alpha-ketoglutarate
undergoes a redox reaction, oxidizing to become
succinyl-CoA
, also releasing
C
O
2
in the process.
Each step generates the coenzyme,
NADH
, an electron carrier which is going to be important in the next stage of cellular respiration, the electron transport chain.