QJ connects question words to the word "and" to create a conjoined question phrase.

         +--------------------Xp-------------------+
         +------Wq-----+------Q-----+---SIs---+    |
         |       +--QJ-+--QJ--+     |   +--Ds-+    |
         |       |     |      |     |   |     |    |
     LEFT-WALL when and.j-q where is.v the party.n ? 

         +-----------------------Xp----------------------+
         +-----Wq-----+-----Q-----+----I*d---+           |
         |      +--QJ-+--QJ-+     +-SIp-+    +--Os--+    |
         |      |     |     |     |     |    |      |    |
     LEFT-WALL how and.j-q why did.v-d you do.v that.j-p ?