Cannot generate Table of Content

What browser are you using and have you tried others?

If you generate one of the supplied sample projects, does the TOC for that appear?

I'm generating a responsive help.

Okay. Let me show you how the page appears when the output is generated.

Keeping my last image as reference, I have created table of content, but does not reflect. How can I get it viewed here? Is my question..

Your first post referred to viewing after compiling the content. However, the images you show are the source files before you generate an output.

Are you new to RoboHelp and expecting to see the generated output within RoboHelp? After 

Content is a bit of a vague term. It can refer to your source files or whatever you have generated (compiled). What are you generating? A CHM output, webhelp, responsive help or a printed document?

After you generate, you can right click to see this menu. Use View or View With to see what you have created. The Output tab might be in a different position on your screen.

I'm using Adobe RoboHelp 2019 Classic.

Yes, when I click on View, I'm not able to find the table of content

By documents I mean, the content that I created on RoboHelp tool. Attaching the screenshot.

2019 New or Classic?

Assuming you mean New, does this occur when you click the View Output icon in RoboHelp?

I also note you say Documents. What sort of output are you talking about?