Informix is quite different in some things. Instead of db2 we have an interactive tool called dbacces. This tool is character oriented an menu driven. But if you want to include sql's for example in scripts you can use the following two options:
dbaccess mydb <<EOF!
select * from schema.my_tab;
Put sql in a file called for example mysql.sql and do:
dbaccess mydb mysql.sql
To answer your second question:
a) onstat -c
b) cat $INFORMIXDIR/etc/$ONCONFIG