Strengths 

As one of the commanders on the Whitebeard pirate crew. Jozu has shown that he is a powerful member of the crew. During the meeting between his captain and Red Haired Shanks, Jozu was not affected by the amazing spirit that Shanks showed. Jozu also has shown to possess incredible ammounts of physcial strength, able to lift a large chunk of ice and throw it at the marine giants. The chunk of ice was so large it dwarfed the giants by a large margin. Though Jozu is a large man, his speed matches his incredible strength. He was able to suprise Crocodile with his speed, and hit him before he could activate his devil fruit powers. He also may have the use of Haki. 
 

Devil Fruit 

 
Jozu has an unnamed devil fruit power which allows him to turn his entire body, or just parts of his body into diamond. This gives him the nickname Diamond Jozu. With this devil fruit power, his durability increases, able to take the worlds strongest slash from Mihawk with no damage. It also increases his strength.