You got a QSL card.
"Pse" is short for "please".
"tnx" is short for "thanks"
If the box next to "pse qsl" is ticked they are asking you to send them a qsl card back, which you would mark with "tnx qsl" because...
If the box next to "tnx qsl" is ticked they are thanking you for the card they have received (that you presumably put "pse qsl" on)
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