How to distinguish hot runner K-type and J-type thermocouples

There is no unified standard for this, and different manufacturers use different standards; the standards of Lilin Company are:
J type positive pole red stripe material iron magnetic
negative pole yellow stripe material copper-nickel alloy non-magnetic
wire sleeve yellow
K type positive pole red stripe material nickel-chromium alloy non-magnetic
negative pole blue stripe material aluminum-nickel alloy magnetic
wire sleeve blue