Ones without a credited author are from me!
Character
Duke's Resolve by redjaybathood
Duke is Not (Really) Nice by himejoshiangels
Duke and Emotional Repression by 5-7-9
Fanon Extremes by strawberrytalia
Duke and Self-Reliance by himejoshiangels
Personal Responsibility by dukethomas
Relationships
Duke's Views on Jason by batboopp
Duke & Damian
Duke & Tim
Duke is a Dick Hater
Duke is Dick's Successor by mattiebluebird
Duke & Bruce
Is Duke in Bruce's Care? by duketectivecomics
Robin / We Are Robin
Duke & The Robin Mantle
Robin and the Making of American Adolescence by Lauren R. O'Conner; screenshotted by 5-7-9
Thoughts on We Are Robin by millylotus
Meta Powers
Summary of Duke's Abilities by dukes-cassettetape
On Duke Being a Meta by arellas
Elaine Thomas
The Karma Incident by himejoshiangels
Extras
Duke in Wayne Family Adventures
Duke is Shaped By Love by ungodlybliss
How Old is Duke? by duketectivecomics
Not all of these are comprehensive and some slightly contradict others, but I find them all interesting and valuable discussions about Duke. If you don't know Duke at all or haven't read his comics, I recommend starting with the Character section!
I will be updating this whenever I find another meta so feel free to send any my way :).