Hello,
As this SCN space is specific to ASE for Business Suite applications, I'd recommend you to use isql/isql64 executables or DBA Cockpit SQL Command line when working with ASE in a Business Suite env.
Having said that, the dbisql executable is located under /sybase/<SID>/DBISQL/bin.
Logged with syb<SID> OS user, your Sybase environment variables should be configured properly to allow you to execute the dbisql without sourcing SYBASE.csh (or.sh) previously.
HTH
Cris