Our son bitten on the nose by jack russell - has punctured the skin and bleeding! should we go to emergency for precaution and tetnis?

Yes: assuming the animal is up to date on vaccinations, your son may need a tetanus booster, depending on his age.

Missing data: If the kid has received the common vaccines for age they would not require a tetanus shot unless it was due. Most infants complete the primary series before 2 & get a booster at ~4-5 and then 10. That 10 yr booster would cover until 20. Since you didn't provide the kids age you need to sort that out. Dog bites can become infected with a variety of germs so close wound monitoring is a must.