TT/Calif needs to know how much of the total capital gain/loss is California-source so that it can tax its share of it. That means all capital gains/loss while you lived there, plus gain/loss when you didn't live there for assets located in Calif such as real estate.
Since all of your capital gain/loss is from stock then only the state you were living in at the time of sale can tax it. That's Texas. That means Calif doesn't get to tax it. So the Calif-source portion of the total capital gain/loss is 0 (zero). Enter that.