How can I split bus in Quartus?

If I understood the question correctly then do this:

1) From the QA port draw a single line out that doesn't connect to anything and name it "counter[0]"

2) Do the same with the QB, QC, and QD ports and name them counter[1], counter[2], and counter[3]

3) Draw a bus line to the SOPC Builder system that doesn't connect to anything else and name it "counter[3..0]"

Quartus II knows that those individual signals connect to the SOPC Builder system since they share the same name. Alternatively you could just wire the four outputs into a bus line within the counter and not have to worry about doing this in the schematic.