what is the meaning when doctor writes E.C.G- wnl ?

WNL is a common medical abbreviation for "withing normal limits." That's good.

E.C.G. is a common medical abbreviation for "electrocardiogram." It is often also abbreviated as EKG.

The electrocardiogram in question did not reveal any abnormalities. That is far from saying that no heart problem exists, however. It is good news, though.

Others
ecg is a scan of your heart, and wnl is within normal limits. or in other words, you are fine. Next time, ask the doctor, He won't think you are stupid
W.N.L is the medical term for within the normal limits expected of you bearing in mind age, sex and previous health problems,
The normal limits for a child are different for the normal limits of an adult,
an e.c.g is the recording of the electric pathway of the myocardium(heart) it consists of a p.wave, a q.r.s complex and an s.t segment, without boring b the pants of you it means the heart is getting the electrical impulse from the right place(sa node in the right atrium)it shows that the ventricles are pumping in unison and adequately and it shows the resting stage of the heart before it recommences the same cycle over and over,
People for example who were having a mi or heart attack as its more commonly known would almost certainly have a raised ST segment on the ecg,this is known as st elevation and if shown up on more than one adjacent lead would indicate very quickly that someone needs rapid medical intervention to prevent death,,
hope this helps in layman's terms