Is belonging a possessive noun

No, the noun belonging is a gerund, the present participle of the verb to belong which functions as a noun in a sentence. Example:

• Belonging is sometimes the most important thing to a child.

A possessive noun is a form to show that something belongs to that noun. A possessive noun is formed by adding an 's to the end of the Word, or just an apostrophe to the end of a plural noun that already ends with s. Example:

• The boy's bicycle was in the rack with all of the other boys' bicycles.