why does Death not comfort the child ? what does this imply about Death's ultimate power ? oh and what item does Death claim from the trash truck ?? why does Death take this item ??

Death wants to comfort the book thief, but it isn't "allowed" (4.22) to do this.

So, Death watches her and follows her when she begins walking.

Death watches as the book falls from her hands and she begins to scream.

Death watches as the book is walked on and then tossed in a trash truck by the cleanup crew.Now, Death jumps on the trash truck, and takes the book, a book that Death will read it "several thousand times over the years" (4.28).

Death can't comfort the child because this isn't his role in whatever cosmic universe he serves in. He can't unfold himself to anyone, he must remain objective and not interfere with how life unravels around him.