You can use the simple test to determine the type of thermocouples that you do not know the types of:

Please view the 4 tables from the following pages:

www.thermometricscorp.com/typej.html
www.thermometricscorp.com/thertypk.html
www.thermometricscorp.com/thertypt.html
www.thermometricscorp.com/typek.html

Using these tables you can find output voltage of thermocouple. For example, if the temperature is 260 C:

E type thermocouple output: 17.9mV
J type thermocouple output: 14.1mV
T type thermocouple output: 12.57mV
K type thermocouple output: 10.5mV

You can use HOT AIR station ( or another calibrated heater) to heat up 4 thermocouples to 260 C. Connect a digital voltmeter between ends of thermocouples and identify types of all thermocouples you have.

WARNING: Use extreme caution when heating thermocouples to extreme temperatures such as 260 C. Such high temperatures will cause skin damage upon contact. Also, some thermocouples have a plastic jacket that will start melting at high temperatures.