Is it possible to upgrade Oracle 8i to 12c?
There is no in-place upgrade possible but the existing exp utility is still supported for importing dmp files.

Some of the issues you need to research are:


I have taken an export from an 8i database and imported it into an 11g with no issues. Importing into 12 should not be a problem but planning is everything!
will you use the same character set?  Often organizations start with western only and need to use UTF16 for more compatibility with other languages.
do yourself a favour and do an install on a new machine with new hardware.  12 requires more of everything, memory, hard drive.
many 8i parameters are not supported so you need to establish if there are any custom settings that you need equivalents for


Of course this would need to be tested.