I'm a fellow user, not a tax expert. The Oklahoma non-resident return is a Form 511NR, which TurboTax can prepare. If you want to read in detail about Oklahoma's Form 511NR and instructions, here is the PDF on the Oklahoma Tax Commission website, where you can view the actual form:
https://www.ok.gov/tax/documents/511NRPkt-20.pdf
You'll see therein that in calculating your Oklahoma tax, Oklahoma first considers all of your taxable income from all sources. By answering screens in the TurboTax state interview, you will designate/allocate how much of each category of your income is Oklahoma-sourced. Oklahoma then prorates the taxable income by taking the AGI from Oklahoma sources and dividing it by the total AGI from all sources.
