KEAM 2017 examination is likely to be conducted in the last week of April, 2017 or the first week of May, 2017. However the notification regarding the examination is likely to be published in January/February, 2017. One of the eligibility criteria is that the candidates should be an Indian national, though PIO (Person of Indian Origin) and OCI (Overseas citizen of India) candidates can also apply. The applicants are categorized in Keralite and non-Keralite categories. Therefore domicile certificate must be required. There appears no relevance to the passport issuing office in such cases. Holding an Indian passport establishes Indian Nationality only.
I have never heard anything like 'corborate certificate' so far. The author may re-check about the exact name of the required document. One possibility may be the birth certificate issued by the Municipal Corporation office which specifies the place of birth.