How to check sybase command line history?
Unless you have enabled history in isql, then you are out of luck.
Moving forward, you can enable it by following these directions:
Check http://infocenter.sybase.com/help/index.jsp?topic=/com.sybase.infocenter.dc30191.1570100/doc/html/san1367605044069.html for details of --history parameter:

--history [p]history_length [--history_file history_filename] – Loads the contents of the command history log file, if it exists, when isql starts. By default, the command history feature is off. Use the --history command line option to activate it.

p – indicates command history persistence; in-memory command history is saved to disk when isql shuts down. If you do not use the p option, the command history log is deleted after its contents are loaded into memory.

history_length – this parameter, which is required if you use --history, is the number of commands that isql can store in the command history log. The maximum value of history_length is 1024; if a larger value is specified, isql silently truncates it to 1024.

history_file history_filename – indicates that isql must retrieve the command history log from history_filename. If p is specified, isql also uses history_filename to store the current session’s command history. history_filename can include an absolute or a relative path to the log file. A relative path is based on the current directory. If you do not indicate a path, the history log is saved in the current directory. When --history_file is not specified, isql uses the default log file in $HOME/.sybase/isql/isqlCmdHistory.log.