How do you simulate a CMYK color mode while maintaining an image in RGB mode?

By activating the Proof Color option by clicking Ctrl+Y or going to the top menu > view > Proof Colors

Just Make sure to activate the Working CMYK Proof by going to view> Proof Setup> Working CMYK and make sure it's checked.

Also by checking the Gamut Warning under the view menu it will make specific gray areas appear in your images which indicate these are the area which their colors will change after converting from RGB to CMYK in printing.

This question I asked today in my lecture. There are a lot of factors that come into play before you print than can alter the color unfavorably away from the original RGB Photoshop file, when you go to print the file,But you can't. You're trying to make two fundamentally different processes look the same

RGB is an additive system, produced by active emitters like the sun or the LEDs in your monitor

It works by supplying light of specific colors, which added together are seen as white

CMY(K) is a subtractive system, removing colors from white light, and you seen what's left

If you combine a yellow filter and a magenta filter, they will pass their common component

which is red, but it doesn't look like a nice pure red from an LED

This is the whole reason "spot" colors are used in the printing process. If you want a color

(on a cereal box, for example) to be some exact shade, you have an ink formulated in that

specific color and use it to print that area of the box. You can't combine generic CMY inks

to yield the same fidelity, no matter what you do

I suggest you feed RGB files to the print driver. It knows more about what the printer

needs and its translation algorithms than you or photoshop do

I hope this will help  you :)