How to expand/collapse all blocks of ruby code in notepad++?

You can use the options under view.

The one that you are looking for is Fold all but you might find some of the other fold/collapse ones helpful.

Short Cuts to collapse & expand :

1) To collapse/fold all blocks - Alt+0

2) To expand/unfold all blocks - Alt+Shift+0

3) To collapse current level - Ctrl+Alt+F

4) To expand current level - Ctrl+Shift+Alt+F

The above question's superset is as follows : Notepad++ expand/collapse block with keyboard

Just to complement the answers posted before, I would like to add that it is possible to collapse the levels of nesting on a level of 1 to 8 with the following shortcut alt + [nesting level] like so:

Nesting level 1: alt + 1

Nesting level 2: alt + 2

Nesting level 3: alt + 3

Nesting level 4: alt + 4

Nesting level 5: alt + 5

Nesting level 6: alt + 6

Nesting level 7: alt + 7

Nesting level 8: alt + 8