USER-EXUTS
Goto to the table tstc and enter the transaction code for 
which u want to find out the User-Exits. Check out the 
program name from the result. Goto SE38 and dee that 
program in display mode. Then search for the string Call 
Cutomer-Funtion. All the result of search are the user 
exits defined there for that transaction.

BAPI
Goto the transaction and check the system->Status->Dbl 
Click on Transaction->Dbl Clk on Package-> Chk out the app 
component (say SALES). Goto transaction BAPI, then chk out 
sales and distribution->sales->salesorder-> open any 
business methods and there you can find the BAPI names and 
u can see them by dbl clcking on them

BAPI
Goto the transaction and check the system->Status-> program 
name. doule click the program name. where u can find the 
string CL_EXITHANDLER. there u can find the bapi