Kdenlive/Manual/Clip Menu/Edit Clip
Edit Clip
This option is available from Project Menu. However, most of the time it appears to be greyed out. I only find is non-grey on a clip that has just been added to the Project Tree.
And if I select the Edit Clip menu item on Video clips nothing appears to happen.
However, selecting Edit Clip on audio clips causes the Audio Editing software Audacity to Open. So my guess is edit clip will cause the clip to open in what ever application is some how set up (in some settings some where) to be the "editor" for this file type.