On Tuesday, Duterte said he had told Paolo to attend the senate investigation if he had nothing to hide, besides advising him not to answer questions and invoke his right to keep silent.
"I cannot answer allegations based on hearsay," Paolo Duterte, the vice mayor of the southern city of Davao, told the Senate.
The Philippine leader has repeatedly said he would resign if critics could prove any members of his family were involved in corruption.
Sen. Antonio Trillanes, a staunch critic of the president, displayed to the Senate panel photographs of Paolo Duterte beside a businessman who was behind the shipment in which the drugs were found.
The president's son-in-law, Manases Carpio, who has also been accused of links to the May drug shipment from China, told the hearing he had no involvement.
The police reject activists' allegations that they are executing suspected drug users and dealers and say officers shoot only in self-defense.
Asked about the tattoo, Duterte said he had one but declined to describe it, invoking his right to privacy. »