Anyone know how to do the Unblockable crossbow are gun attack for ezio?

The unblockable crossbow attack is called "Requiescat in Pace"

Requiescat in Pace
B+K

Hold vertical attack and kick and Ezio will prepare the flaming bolt. The only escape for your opponent is to sidestep or duck. For regular crossbow attacks:

Standard Crossbow
6 B+K

Low Crossbow
2 B+K

Evade Crossbow
4 B+K

Oh, I should mention what the numbers mean, just in case. While some games describe directional input in a radius of motion (Street Fighter's Ryu has quarter-circle forward and then punch to do a fireball) or specific angles (Mortal Kombat's Sub-Zero has down, down-forward, forward then punch to launch an freezing blast), Soul Calibur uses a numeric system. Look down at a number pad (your keyboard, a calculator, etc.) and you'll get the idea. So if Ryu and Sub-Zero were in Soul Calibur, their projectile attack motion would be "236." So 5 is the neutral middle, 6 is forward, 2 is down, 4 is back from your opponent, and so on.