Typical Landing Newel Post Detail
The typical detail for fixing a landing newel post is to notch the newel post over the edge of your floor joist inline with the top newel on the staircase and double bolt the newel post to the joist.
Fitting a landing newel post during a staircase installation is a very important part of the landing balustrades strength - I suggest a qualified carpenter should carry out a staircase makeover or new install.