The Instructions part of ITR 2 states that the country code is the ISD code of the country from which the foreign income is received. You can get to read the instructions in the following page of the I-T Dept. or from the ITR form itself.
https://www.incometaxindia.gov.in/Supporting%20Files/ITR2018/Instructions/Instruction_ITR2_2018.pdf
Hope this helps. Thanks.
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