How to port a plugin

I am really interesting on how to port a spigot/bukkit plugin to sponge one
could anyone can help me?

Step 1: Change the dependency from the Bukkit API to the Sponge API
Step 2: Change all the red underliney bits to the Sponge equivalents and add a @Plugin annotation

The answer to ‘what is the Sponge equivalent to X in Bukkit’ is really just ‘how do I do X in Sponge’ which is an answer best found at the docs.

Also. If the plugin isnt yours, then check the license to make sure you can make a port of the plugin, failing that, ask for permission from the current dev(s).