I digged around the intetnet and find the answer.
const publicKey=await openpgp.readKey({ armoredKey:publicKeyArmored });
const td=new TextDecoder();
for(const {selfCertifications} of publicKey.users){
if(selfCertifications.length==0)continue;
const latestCert=selfCertifications.sort((a,b)=>
b.created.getTime()-a.created.getTime()
)[0];
if(latestCert.revoked)continue;
for(const {name,value} of latestCert.rawNotations){
console.log(`${name}=${td.decode(value)}`);
}
}