If you are his second cousin, he is your second cousin
Asking about your second cousin's cousin's cousin is asking about a complex but poorly defined relationship. Are the cousins of the second cousin his first cousin, second cousin, fifth cousin twice removed, or something else. It is likely that a cousin's cousin's cousin is not related to you at all. It is also possible that your second cousin's first cousin's first cousin is also your second cousin.
Your second cousin's niece is the daughter of your second cousin's brother or sister. Your second cousin's brother or sister is also your second cousin, so this question is the same as "How are you related to the daughter of your second cousin."The daughter of your second cousin is your second cousin, once removed.
Your first cousin's second cousin may be your second cousin as well, or may not be related to you at all.
Your child is your cousin's second cousin. (And he/she is your child's second cousin)
Your second cousin is your parent's cousin's child. You and your second cousin share a great-grandparent (not a grandparent).
He is your second cousin also
No, your father's first cousin is the parent of your second cousin. Your second cousin is your father's first cousin, once removed.
The child of your second cousin is your second cousin, once removed.
Your mother's second cousin is your second cousin, once removed.
Your second cousin's daughter is your second cousin, once removed.
Your second cousin's child is your second cousin, once removed.