Replacing a top cap on a concrete block fence

Two of the top caps on my concrete block fence has come off. The old mortar has all come off of the caps and the top of the fence blocks.
What is the best way to reattach the top caps? What is the easiest good way to reattach the top caps? Thank you in advance for all replies.
I am TERRIBLY cruel to my cat. I actually cut of the ends of
his toes. It\'s just the hard, dead part that grows back but
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