How to find out the frequency and tact of RAM?

Question

laptops

I downloaded CPU-Z, but the memory tab is not available for some reason.
How can I find out the characteristics of my RAM in order to choose the second bar?
As I understand it, the first one is built-in and cannot be replaced, but inside, there seems to be a slot for another one.

And as I understand it, if I have 4GB of built-in RAM, then I need to buy only 4, not 8?
I read that only 4+4 or 8+8 will work dual channel and that 4+4 is better than 4+8.

Answer 1

Aida63, ​​You can also look in the BIOS.
4 + 4 is better if they work in two-channel mode. Whether they will or not - look at the character of the laptop by model

Answer 2

SPD tab in CPU-Z