As suggested in https://github.com/boostorg/boostbook/pull/26#issuecomment-2108504800

doc/Jamfile.v2

@@ -198,7 +198,7 @@ explicit libraries ;
 
 xinclude tools :
     ../tools/quickbook/doc//quickbook
-    ../tools/boostbook/doc/boostbook.xml
+    ../tools/boostbook/doc//boostbook
     ;
 explicit tools ;