Today I noticed a very small gas leak from a screw on gas filler cap.
The gas seems to be leaking from thread of this tiny screw on lower sider of gas filler cap.

Can some one please suggest me how can I fix it ?

umm replace the cap ?

yeah. or duct tape. or ignore it if its that small. did you just smell it?

You probably HAVE TO replace the cap or else you would fail the gas cap test at the emissions. (assuming you have to do that test)

even if he doesnt fix it, hes prob gonna get the cel light on for evap codes, and get lower mpg. Its only 6 bucks fix it. If its the neck itself you can buy one here for cheap and replace that.( I have one for sale by the way)

Lots and Lots of Teflon Tape

Gas is leaking from the fixed plastic cap which I think binds & aligns the tank with filler hole & car's body. Is it something easy to change?
Its *NOT* leaking from the cap which needs to be opened everytime to fil the gas. I am getting EVAP code, first I thought its EGR again then I figured out leak and hopefully fixing leak will take care of code also.

Yah if its what I think it is, its the filler neck. If you check behind the wheel there is a cover, remove the cover you should see the tube. I recently replaced mine as well, it was rusted do to weather here in Cleveland.

If all else fails, get out the welding equipment and go for it.

Try to stand no closer than 100 feet or you may be in for a surprise!