敲敲 is the reduplicated form of the verb 敲 (qiāo, 'to knock'). In Chinese, verb reduplication (VV pattern) adds a sense of doing the action briefly, lightly, or in a casual/tentative way — like 'give a knock' or 'knock a little' rather than a forceful or prolonged knock. It often carries a friendly or polite tone, as if you're not imposing. This form is common in everyday requests and suggestions.