You should request John's naturalization intent & petition as it will have his place of birth. http://www.archives.gov/research/naturalization/index.html
Your ancestor's social security form SS-5Form should have his place of birth and parents names.
John could have come thru an US port as Janos, Jan or Johann. Did you look in www.ellisislandrecords.org
Any one of the BANKOSs and BANKOSZs related to your ancestor?
BANKOS^ in Slovakia's phone book http://www.zoznam.sk/hladaj.fcgi?co=telzoznam&s=bankos&a...
No BURKIS or BURKAS surname in Slovakia.
BURKAS arriving NY Ellis Island from Rokamezo, Hungary now Lysychevo, Ukraine.
I want to say that your reply is only to me and not to the previous poster, marksabol21