I came up with one answer off the top of my head, but figured I’d put a more complete list from my bookshelves here.
Killashandra by Anne McCaffrey. This was my answer to the tweet as it is on my desk to read along with Crystal Singer, its immediate predecessor. In the 70s and early 80s I read a lot of McCaffrey, but I did not read this trilogy.
K is for Killer by Sue Grafton. Arguably, I should have thought of this first because it is the obvious one. The Kinsey Millhone books provide us with every letter but Z.
Kitty and the Midnight Hour, along with twelve of the other thirteen books in the Kitty Norville novels. Except for Low Midnight, the only book where Kitty is not the principal character, all the books in the series start with Kitty. These are my favorite werewolf books. They initially won me over because I was doing late-night radio at the time the first one was released, just like the lead.
Killing Orders by Sara Paretsky. This is the other detective novel on the list. I’m surprised more detective novel titles do not start with killing.
King of the Murgos by David Eddings. As with detective novels, I am surprised I do not have more fantasy books starting with king or knight.
And that is all I found. The list doesn’t quite double if I exclude and initial “The” from a title. I have several “The King” and one “The Knight”.
Wonderful!