I need help in flashing CircuitPython in nRF52840 DK can anyone help me out

What error does it show?

You must be having the CircuitPython binary right! From your message what I understood is that you need help loading it to the board.
Can you explain what exactly you are trying to do?
If you are an absolute beginner then follow the instructions given the link:
https://circuitpython.org/board/pca10056/

Which bootloader to download from the given link and how do I flash it in the nRF52840 DK.

github.com/.../0.8.3

Which one out of the following

pca10056_bootloader-0.8.3_s140_6.1.1.hex

pca10056_bootloader-0.8.3_s140_6.1.1.zip

https://downloads.circuitpython.org/bin/pca10056/en_US/adafruit-circuitpython-pca10056-en_US-9.1.1.uf2 

is the above link a bootloader. How to flash it into the board.

you can program it by

nrfjprog -f NRF52 --program pca10056_bootloader-0.8.3_s140_6.1.1.hex --verify --reset

make sure you have installed nrfjprog installed
https://www.nordicsemi.com/Products/Development-tools/nRF-Command-Line-Tools/Download

Nope it's not the bootloader. It's a uf2 image of circuitpython. You need uf2-bootloader in-order to run that application

The flow is as follows

resetHandler -> UF2_Bootloader -> Circuit Python image (*.uf2) 

I tried nrfprog it is showing error. Can you help me in solving that error given above

I am not a windows user! Dont know how to help you with that. But I would strongly recommend you to do the following things

1) Unistall the nRF Command Line Tools
2) Check which version of windows OS you are using (32/64)
3) Download the nRF Command Line Tools by checking the correct OS version
4) Install the nRF Command Line Tools

ok

Still getting same error with nrfjprog. What is the process to install it. I tried in fresh windows.

Still getting same error with nrfjprog. What is the process to install it. I tried in fresh windows.

Your error message suggests a DLL failed to load. This appears to be an issue with your tools installation. You could try another board, but it doesn't sound like a board issue.

If you've followed the install instructions to the letter, and it doesn't work, it's worth raising a problem report with the developers.

Do you have link that can help me in proper installation of nRF-commandline-tool

Unfortunately no. You should try to follow any official instructions. If that doesn't work, discuss with the owner (for instance, if it is on GitHub, you can raise an issue). If it is on a manufacturer download page, then raise an issue with their tech support (or their discussion forum, since they may know what the issue is).

Also, there seems to be some issue with the screenshot, a discrepancy regarding MicroPython and ESP32, compared to what would be expected (see the comment from mp2100 above).