How do I post notices for this quest? I can't find where or how to do it.... can anyone help me on this??? Thanks in advance

There are 2 place you can post (not sure if there's more) in tranquil seacoast 3:

1st place to post is near the portal to tranquil seacoast 2 - the umbrella with coconut
2nd place to post is east of NPC cluster - shells on pole

move your mouse over will give you action icon - magnify glass

the 3rd one is at coord: 3345, 2420