Well the LHS is normally the pax as I'm sure you're aware, and that seems to answer the question in your title for this thread. Reading between the lines though, it seems you're wondering whether the PIC can sit there.
I stand to be corrected on this one, but I don't think there is anything in the primary rulebooks about which side you should sit on, simply because in the past (and probably currently for all I know) it has been type specific.
There are rules about qualifications required in order to touch the controls, about following the flight manual, and about maintaining a C of G within limits, but not as far as I know specifically about which seat you must fly from.