Do a google search for this
liteon 3 1/2 digit display
You are looking for datasheets like thishttp://optoelectronics.liteon.com/en-us/api/DwonloadFileHandler.ashx?txtSpecNo=DS-30-97-339
which shows you more clearly the kind of connections you are looking at. This one appears to have a few more decimal point/colon connections than yours.
The part either be common cathode like this, so you put ground on a pin and poke around with 5V thru a resistor to see what turns on, or it will be common anode, so you put 5V on a pin and poke around with ground thru a resistor to see what turns on.
Make notes as you go.