First, you need the Byakko Badge ( fight the real Byakko Leader ).
Your digimons combination must be under level 30 to talk to the DRI Agent in Protocol Ruins. Keep going left until you end at a dead end ( one more left after you see the ladder which leads to Baronmon's place ).
After talking to him, now go to Bulk Bridge which is in North Sector. Cross the bridge ( the bigger one which leads to another island ) then go up and up until you see Paildramon. I have fought Paildramon alone with my level 23 Kotemon. After you win the battle, Paildramon gives his DDNA. Go back to the DRI Agent and he'll add Veemon as your partner. And then you go to Dr. Kadomatsu or Piximon to change one of your digimon. You now got Veemon as your partner!
Tip : If you found it hard to train him, just fight a strong monster and make sure he starts first, then quickly switch to a stronger digimon and fight it. Both will get a divided EXP but still worth to train a weak Veemon.