Knock adjectives are listed in this post. Each word below can often be found in front of the noun knock in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing KNOCK.
brief, brisk, discreet, double, faint, familiar, firm
first, gentle, good, great, hard, hasty, heavy
hurried, impatient, insistent, knock, light, little, loud
low, nasty, peremptory, polite, quick, quiet, second
secret, sharp, single, slight, soft, sudden, tentative
third, thundering, timid, unexpected
Hope this word list had the adjective used with knock you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.