Nuke offers several ways, including some useful hotkeys, to focus on the area of the Viewer you need to see.
Hold the middle mouse button and drag on the display (you can also use Alt+drag). The frame follows the mouse pointer.
NOTE: On Linux, Alt+drag may not work as expected. This is due to the default window functionality on Gnome. To get around it, you can use the 
(Windows) key instead of Alt when panning.
Alternatively, you can change your window preferences on Gnome to fix the problem:
1. Select Applications > Preferences > Windows to open the Window Preferences dialog.
2. Under Movement Key, select Super (“or Windows logo”).
You should now be able to pan with Alt+drag.
Click the middle mouse button or press F.
| 1. | Move your pointer over the area of the display on which you want to zoom. |
| 2. | Drag the mouse while pressing the middle mouse button and the left mouse button. |
OR
Press the plus button (+) repeatedly until the frame attains the desired scale.
OR
Select zoom in from the zoom dropdown menu 
in the top right corner.
| 1. | Move your pointer over the area of the display from which you want to zoom. |
| 2. | Drag the mouse while pressing the middle mouse button and the left mouse button. |
OR
Press the minus button (-) repeatedly until the frame displays at the desired scale.
OR
Select zoom out from the zoom dropdown menu in the top right corner.
Press Ctrl+1 (Mac users press Cmd+1).