I have 3 Bowens Monolights, Model 400D. I now have an Fuji XPro1 digital camera. What I would like to do is to fire one of the monolights via a transmitter on the hot shoe of the camera and have a receiver plugged into the one of the Bowens lights, which has a 6.3mm socket. The other two should fire off automatically, as they have a Monocell plugged into them. That's if I can get the one light to fire. What flash trigger would work with this setup?
Any basic radio trigger will work for this setup. The only issue may be the sync voltage of your monolight. Most radio triggers will not work correctly if the voltage is too high.
Another option is to have all your monolights run as optical slaves and trigger them all by firing a speedlight on your camera at the ceiling (or towards one of the flash heads if you are outside).
Generally speaking, any flash radio trigger that works as a transmitter with the XPro1 hotshoe, and that has a receiver you can plug into the 6.3mm socket on the monolight.
The main thing to look for with manual radio triggers with mirrorless cameras is whether you can get the on-camera unit to be a transmitter. The majority of the manual radio triggers out there are designed to work with Canon or Nikon dSLRs. And some of the transceiver units were designed to auto-switch into transmitter mode by sensing a signal on something other than the sync pin. Which pin and the type of signal is system-specific, so the Canon units work properly on Canon and Nikon units work properly on Nikon. But a Nikon unit won't work properly on Fuji X because the pins/contacts are placed different from each other and no contact is actually made. And a Canon unit won't work properly on Fuji X, even though the pin/contacts line up, because the signal is on the wrong pin. Upshot: with Fuji X, the on-camera unit never goes into transmitter mode. An example of a trigger like this to avoid would be the Yongnuo RF-603 (mark I).
So whatever trigger you're interested in, it's probably good to find a Fuji X messageboard and ask around or search to see if the one you like is compatible with the XPro1, first. Or, just make sure either that the transceiver unit has a way to explicitly set it into transmitter mode, or that there are separate dedicated transmitter and receiver units so there's no autoswitching you have to override.
Also be aware that Canon/Nikon units may have an odder fit and more difficulty seating properly on the Fuji X hotshoe. Sometimes using a Nikon unit will work better than trying to use a Canon.
With the receiver units, the only thing you need to discover is if a receiver unit in the triggering system has a sync output port, what type of port it is (PC, 2.5mm, and 3.5mm being the most common), and then get the correct cable to hook that up to your monolight (e.g., a 3.5mm -> 6.7mm cable).
For a list of some popular manual-only radio triggers, see: http://flashhavoc.com/flash-trigger-guide-manual/