I have a question. When Reiksguard knight is blocking the atacking unit receive 2 damage token. But when this unit has 2 lifepoints its dead or reiksguard is still reciving damage from this unit

The unit killed by Counterstrike is done so when the counterstriking unit is declare defender. Thus its done before the dead unit had a chance to coutribute with its power to the attack pool. So in your example the Reiksguard knight wuld not get any damage from the opponet.

More specifically -

1. Player A declares which zone they are attacking and attackers
2. Players may take actions
3. Player B declares defenders, Counterstrike deals damage
4. Players may take actions
5. Combat damage is counted and assigned
6. Players may take actions
7. Toughness cancels assigned combat damage all other combat damage is applied and its effects resolve, units with damage counters equal to their HP are removed from play, Burn tokens are placed on the city if necessary.
8. Players may take actions