Use transaction SE30 to run an online transaction and see how it performs in ABAP, Database & R/3 System.
Put the transaction code in and click the execute button. When it finishes, click the back button to take you back to the first screen, and click Analyze at the bottom.
This will show a graph with the time used, split between ABAP, Database and R/3.
You can also click Goto --> Hit List --> Standard and this will show exactly where the time is used in the program. Sort by Net% field in descending order to see the longest time consumer.