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The default two conky files that are called upon startup are these:
/usr/share/conky/conky_shortcuts_live_maia
/usr/share/conky/conky_maia
These files are called by the executable start_conky_maia that is referenced in your i3 config file.
In both of these files there is a font entry, which you can use to change the font family and font size.
In my opinion, the best way would be to copy the contents of these files in your home directory - as other members have already mentioned above - and edit your i3 config file so that it points to the conky file in your home directory at startup.