I have a idea for a small project where I will try to transfer real time sensor data that is captured and converted to digital signal using MCP3008 to the NodeJS server that is installed on Raspberry PI. 
My question is: what is the most efficient and/or fastest way for data transfer from Python program to NodeJS server to be displayed in webpage.
Thanks for you advices
Depending on the amount of data and the complexity/simplicity that you want to achieve, you can e.g.

hit HTTP endpoint of your Node server from the Python program every time there's ne data
connect with WebSocket and send new data as messages
connect with TCP once and send new data as new lines
connect with TCP every time when there's new data
send a UDP packet with every new data
if the Node and Python programs are running on the same system then you can use IPC, named pipes etc.
there are more ways to do it

All of those can be done with Node and Python.
Data transfer between Python and NodeJS in Raspberry Pi