Confusion with output wiring and signal conditioning
Do the D and S represent a MOSFET transistor?


Yes they do.


  Does this instrument have 2 different pulse outputs (F - Source and F
  - Sink)? What could it be the reason?


The outputs are open drain with an N channel MOSFET pulling the output to ground AND an open drain with a P channel MOSFET pulling the output up to +US.


  If I use for instance F – Source output should I use GND or AGND?


F_Source is the P channel MOSFET output  - it pulls-up to +US and "your" load connects to ground.


  Why do I need extra pull up/down resistors?


The outputs are open source outputs and these require a load or pull-up/down resistors to convert the output into a switching voltage.


  Finally I couldn't find out what is the pulse output voltage with a Vs
  supply voltage (15-24V). If for instance the supply voltage is 24V and
  I want a pulse train with 8V 0V; can I then simply use a voltage
  divider or should I use an op-Amp?


You can use a voltage divider to give you a pulse at 8 volts - that's probably the simplest way to do it but it all depends on what circuit the 8 volt pulse connects to.