I'm new to inkscape and to learn it I'm watching some videos on it.
In one video they are showing the merge gradient tool.
On a line they can double click to create a node, in my version (latest) it won't let me do that.

On the video, a cross appear when they hover over the line. For me it doesn't.
http://imgur.com/jBim3uL

Is there a new way to do this? The video is dated from 2015.

I guess you mean the Mesh Gradient tool, but please confirm. Is the video publicly available so that we can check exactly what they're doing?

What system (OS) and Inkscape version?

Are you using the gradient tool?

Works here on win8.1 /64, Inkscape 0.92.1 r15371

Yes I meant the mesh gradient tool.

This is the video: https://www.youtube.com/watch?v=uxcbUX4J6rk
I think start at 6:20 is the best to understand it. (at 6:44 he does it)

I have windows 10 and I downloaded 0.92.1 (yesterday from the main site, latest version)

The video at 6:20 shows the gradient tool operating on a radial gradient.

Make sure you are using the gradient tool , not the node editing tool .

I'm using the gradient tool. But the cross you see when you go over the line, doesn't apear for me.

edit:
https://youtu.be/qvfbBTRYzR0

It appears you are trying to edit a radial gradient with the mesh gradient tool.

I frequently am unable to add new gradient stops or nodes by double-clicking on the handle. So far, I haven't been able to figure out why. So instead, I use the button on the control bar, for adding more stops. The object with the gradient has to be selected, for the buttons on the control bar to become active (otherwise they're grayed out).

Edit
I never have noticed about the pointer icon changing, but I'll check for that, the next time it happens. (Of course it doesn't happen when I want it to. )

I have the same issues Brynn, clicking it (actually double clicking) doesn't usually work for me either, the gradient line is so slim that it's hard to hit it on target maybe, not sure what the issue really is. I also use the toolbar to insert new stops. But, you have to remember to have the object selected, and then click on the word 'Gradient' from the toolbar so that it opens the Gradient toolbar.