Adding the Knockout or "KO" feature to a question in the survey means that it is a requirement for the supplier. Not answering, or failing to meet the minimum requirements of a KO question could lead in disqualification of a supplier's offer.
In Negometrix, a supplier who submits an offer with a KO question unfilled will still be allowed to submit their offer. However, in the evaluation dashboard there is a column for "Knockouts Missed" in which you can see how many and which knockouts the supplier missed, therefore allowing you to disqualify their response.
KO should be added to a question that is absolutely mandatory for the supplier to answer properly. For example, terms and conditions, or forms that they cannot participate with are good examples of KO questions.