Daiwa Reel Nib

Forgive me for being so stupid but I need some knot tying advice for a Daiwa 47H Reel?

I feel stupid asking this and I know I should. On the Spools of the larger big water Daiwa Baitcasting reels their is a nib on the spool. What is the nib for? How should I tie the line to the spool, what is the best knot? I want the reel setup to catch 6 foot sturgeons.
I know what an Arbor knot is but it just doesn’t seem very strong.

Arbor knot is fine. If you get spooled by the fish its not going to matter much what kind of knot you used to tie onto the reel. If you find that the knot you used slips, take it off and tie the opposite way. It will lock up then. Unless your using braided line it has a tendency to slip any way you tie it. When using braid on my baitcasters I use a mono or flourocarbon backing to keep the slippage from happening then tie on the braid, then add a flouro leader.