Sorry for the late reply! The keys are shown in the "Help Menu," and they should be: the left and right arrow keys (for highlighting the buy or sell button, for example if the "buy" button is highlighted currently then click the right arrow button on the keyboard in order to highlight the "sell button", the highlighted button will have a yellow and white flashing border around it), the 'X' key (for selecting the currently highlighted button, which is either the sell or buy button), and the 'Z' key (not really needed but this is used to "skip" a turn without buying or selling).
I hope this helps!