Fine.
On top you see

the number of found rows (in my case 101)
and the query used by phpmyadmin to retrieve these rows

Click the SQL tab now to open the editor and make a screenshot

I asked you to open the ossn_object table

What different subtypes do you see in YOUR table?
How many rows does it have?

I enter phpmyadmin, this is not a problem. What’s the problem is that I don’t know exactly what to look for in it and how to look for it.

Ok, so let's look into your code ...
line 14: is creating a new instance of the OssnWall class
line 15: is calling the GetPosts function of that class and passing an array of parameters
Let's ignore these extra parameters for now and see what GetPosts does by default...

That function is located in components/OssnWall/classes/OssnWall.php
We see: a database SELECT is being prepared here, with only 2 parameters before the main searchObject function is called at the bottom

At the top of the class file we find that class OssnWall extends OssnObject, so it's obvious we should have a closer look into the ossn_object table.

So, please start your phpmyadmin and do that.

Okay, by default phpmyadmin is displaying ALL records, so your first task is to build a SELECT query with the same parameters as used by the the GetPosts function, reducing the result to records of subtype = 'wall' only

Please post that query here ...

Enjoy watching TV, we will continue tomorrow. Phpmyadmin is not a problem.

Okay, so we have to refine Arsalan's code to exclude the group records.
But that would take a little time and I want to watch some TV now ;)
So let's continue tomorrow.
Meanwhile you should create some group entries we can work with.
And if not already done, please make yourself familiar with phpmyadmin because we need to have a look into the database
And please have a look into the GetPosts function Arsalan is using in OssnWall/classes to get an idea what's still missing

Yes, only on the main wall.

But you said, you do not want to delete any post on the group wall - only on the main wall, is this correct?