> My question is if i put SFTP stored procedure in DB, then my SFTP connection works on behalf of which machine? DB or OAS?
Once a stored procedure runs on the DB server, the processes will be from the db server, UNLESS all it is doing is fetching data for your OAS to actually send the FTP. We can't know which, as you did not specify what forms built-in or db packages you are using to send the file.
>Second, if i do webutil host() command, in which directory, i should put my 'shell script', db or oas?
Webutil is running from the OAS server. Host of course can only refer to the OAS server. Whether you should put the script in the DB or OAS? We can't tell - you did not specify what is script needs to do, and more importantly the actual problem you want to solve.
> Third, how to know pwd (working directory) of my form?
There is an oracle home where forms is installed, but you should set any environment variables implicitly if they are important to you, instead of relying on Oracle.