How many secondary oscillators are connected to my PIC24F
Take a look at the link your provided for the PIM module. The "Pin Mapping" section explain this:


  There are several device pins that don’t have a one-to-one connection
  to the ICE connector. Some are hard-wired to a certain location, while
  others are mapped to the connector through jumpers.


In the Table 1, you can see thant the SOSCI and SOSCO pins are not connected to a PIM pin.



The Crystal on the Explorer 16/32 will not be used. Only the one on the PIM.