let UserInfo=[],
    line=[];
for(const list of req.body.list){
    line.push(
        new Promise((resolve,reject)=>{
            con.query('foo bar blahblahblah',(err,rows)=>{
                if(err){
                    reject(err);
                }else{
                    //do stuff push data to UserInfo
                    resolve();
                }
            })
        })
    )
}
Promise.all(line)
.then(()=>{
    res.status(200).send(UserInfo)
},(err)=>{
    console.log(err);
    res.sendStatus(500)
})