I see the "Duplicate" button only for the slides. How do I find it for the textbox? Inkscape, for instance, has such option to create the new object right at the same place as the source object. This is what I am asking for.
If you want to duplicate a textbox on a slide, just select it, then copy and paste. If you paste it into a different slide it will have the same properties as on the original (positioning, size, etc.); if you paste it back into the original slide it will be offset slightly so that it doesn't completely overlap the original. No duplicate button because this feature is covered by copy/paste.
Select the shape (or click within a text box then press ESC to select it) Press Ctrl+D to duplicate it. Press the up arrow twice, left arrow twice. It's now aligned with the original
If you need more than one duplicate, keep pressing Ctrl+D after the above. Further dupes will be aligned with the first.