go to help -> debug window -> console and type "listaddressgroupings"
you get an overview of all the addresses in your wallet.
to get the private key for an address type:
walletpassphrase "yourpassphrase" 600 (i hope your wallet is encrypted
)
dumpprivkey PtsAddressHere
you might want to move your whole balance to one address before so you don't have to handle multiple keys. just create a new one and send everything there.
@Gekko:
i think there's not really another way. maybe a routine which reads the pts wallet.dat could make it more user-friendly, but in terms of security a transfer of the private keys is the only way to prove that you own the pts