There are three standard tunings for it. One is like the top four strings of a guitar. DGBE. This is sometimes known among banjo players as "Chicago" tuning.
The second is in fifths like a tenor banjo. CGDA or GDAE. The third is like a plectrum banjo tuning.CGBD (Eddie Condon used the last one with trad jazz bands).

The instrument that is used sounds different with these three tunings. I find that a tenor
guitar will accommodate one of the above mentioned tunings better than the other two.
The Eddie Freeman model is built like a Maccaferri or Selmer Django style instrument.
I don't know which tuning is best for this. Also, Ukulele Ike (Cliff Edwards) fashioned
a resophonic four stringed instrument which probably he strung like a uke. However,
it might accommodate a tenor-tuning as well.

Frank Hamilton