Watchlist Font Size
To do so, click on the table button in the upper right corner of the screen. There will be two options, "Zoom In" makes the table text larger, and "Zoom Out" makes it smaller.
Scrolling Ticker Font SizeIt is also possible to increase the scrolling ticker font size. To do so, open up the app preferences by pressing Cmd+, (command and comma keys) or by going to the Stock + menu at the top of the screen.
Click on the "Ticker" tab, and there will be a Font Size (Ticker Height) slider.