I purchased 20 shares of GLD back in Nov 2020. I did not sell this stock, but Turbotax is showing it as a sell with missing cost basis. On my 1099, this stock is listed under a heading of "UNDETERMINED TERM TRANSACTIONS FOR NONCOVERED TAX LOTS". The proceeds are $1.20. How do I determine a cost basis on a stock I did not sell? Should this have been placed somewhere else in Turbotax?
If the proceeds were only $1.20, enter the cost basis as $1. This approach will not have any effect on your taxes or create an error with the IRS (the net gain/loss will be "0").
This was probably the "sale" of a very small fractional share - the result of a reinvested stock dividend - that was automatically processed by the brokerage firm's computers to simplify their record keeping.
See https://www.spdrgoldshares.com/media/GLD/file/SPDR-Gold-Trust-Tax-Information-2020.pdf for the calculation and note that GLD is considered a collectible which is taxed at a long-term capital gains tax rate of 28% (if you held the fund for more than one year).
Also note that the reason you have proceeds when you did not sell, is that the fund sells a small percentage of gold to cover fund expenses (and those expenses are currently not deductible since they are considered miscellaneous itemized expenses).
Frankly, given the low figure of proceeds ($1.20), you are probably just better off entering a zero basis, if you are going to enter the transaction at all.