Am 28.02.2019 um 14:03 schrieb Periklis Gogas:
It is the default sample data files included in Gretl.

Up till now, you go:

File > Open data > Sample file and you get a list of sample files included within Gretl.

Well, not quite. Usually there are several tabs in that window. Do you see the tabs? Which tab do you mean?
If you don't see the tabs (or the ones you need), you could try the network icon/button at the top (the 3rd one) to download the sample data.

-s