How many carbon dioxide molecules are liberated after each cycle of the Krebs cycle? For a single glucose how many carbon dioxide molecules were already liberated by the aerobic respiration at that point?

Each round of the Krebs cycle liberates two carbon dioxide molecules.

At the end of the cycle all carbon atoms from the original glucose molecule degraded in glycolysis are already liberated incorporated into carbon dioxide molecules. That happens because for each glucose two pyritic acid molecules were made by glycolysis.