Nvidia RTX 2080 ti

[Kefdesignn]

Currently I am using hp z8 g4 workstation, it has 3 GPU slot, and I already install one RTX 2080 ti Gigabyte brand, now I have plan to install one more GPU so I have some doubts 

1. Is it possible to install different volume and different  brand GPU

2. And should I change power supply ..? 
3. should I add extra cooler..? 
4. now I am using only one processor so should I install second processor while installing new GPU

[DGroves]

1. Is it possible to install different volume and different  brand GPU Yes, but why?

Unless you plan on using only the "CUDA" cores on the second card, it's pointless to install a second consumer video card as SLI does not work on hp workstations unless you have a approved "QUADRO" model video card

2. And should I change power supply ..?  depends on what your current supply is, and what you plain to install in the system

3. should I add extra cooler..?   to what? and why?

4 now I am using only one processor so should I install second processor while installing new GPU      Again why? for what purpose?

[Kefdesignn]

1. Why , because now I am using adob after effect and lumion and other rendering software, so its taking longtime for rendering and while rendering time I am not able to do other worked , its frequently getting slow moving, 

2.now I am using 750w

3 if I am installing this one more graphics card that will cause to heat will be high 

4. right now system dosnt have that speed and it’s not helping me to use multiple work in same time 

and also I heard that if I should not install other processor some PCI slot will not work. is it true ..? 

[DGroves]

there is this thing called documentation that HP makes available for their products i highly recommend that you take some time to read the available documentation on your model workstation as it covers all of your questions about power supply, power draw, power consumption of hp approved video cards, and pci-e slot availability using one or two cpu's and if additional cooling is required for different configurations 

https://support.hp.com/us-en/product/hp-z8-g4-workstation/16449803/model/16449805/manuals

if after reading you have a question, post it and we will try to clarify the hp documentation in regards to your post

in regards to your software related questions:

https://www.pugetsystems.com/recommended/Recommended-Systems-for-Adobe-After-Effects-144/Hardware-Re...

https://lumion.com/blog/lumion-computer-advice-for-faster-3d-rendering.html