I am a partial year resident of OK and sold my house in AR when moving to OK. I did not sell an OK property but they are asking about cap. gain for OK.

Prepare your Part-Year Resident return for Arkansas first, then your Part-Year Resident return for Oklahoma.

You should be able to 'Allocate' unearned income (like Capital Gain) and confirm the amount that TurboTax has transferred in each state interview. 

Some states take the total amount from your Federal return, then ask for state amount.  This is what Oklahoma does on their Form 511NR.

Here's more info:

https://www.ok.gov/tax/documents/511NRPkt-17.pdf