don't know what to do 

It means what you don't know from what you wanna do in that moment what is happening..

Like for example!

When you have a problem and you don't know how to solve it:
I don't know what to do!

don't know what to do by Heysdj October 18, 2019

I don’t know what to do

UD Jews, I’m talking to you guys

I’m very confused and am unsure as to what I should do.

My friend said I know the truth and that I shouldn’t be worrying. But things are getting really tough.

Will the stock market crash soon or will WW3 break out soon? That would kinda give me an advantage.

I don’t know what to do.

I don’t know what to do by Zatarain’s Root Beer Drinker January 12, 2023

I don't know what I'm going to do with you! 

Significant other is fed up or exhausted with the idea of you being around them.

Justin, you are getting to be too much and I'm confused about how I should handle you! You have made me mad/annoyed for the last time!!
("I don't know what I'm going to do with you!" is to be aggravated or annoyed by one's actions)

I don't know what I'm going to do with you! by anonymous November 18, 2022

I don't know what to tell you 

A phrase used to tell another person to politely say, "I have no interest in continuing this conversation or listening to you complain." In its hardly ever used long form, it would be used as, "I don't know what to tell you to get you to shut up." Extensively used when people present you with a problem, you offer advice to them on viable solutions, but they come up with excuses why they can't follow your advice.

Person A; "complain, complain, complain. My car broke and I can't get to work now. And boss says he'll fire me if I miss another day!"
Person B; "Take the bus."
Person A; "There's no bus route within a quarter mile, and my feet hurt so much."
Person B; "Take a cab."
Person A; "I can't afford a cab with these car repair bills!"
Person B; "I don't know what to tell you."

I don't know what to tell you by Edward C. Microwagious IV May 31, 2010

i don't know what to search

Well, if you don't know what to search in the urban dictionary, why not try to solve this problem:

Evaluate ∬ yz+4xydS where S is the surface of the solid bounded by 4x + 2y + z = 8, z=0, y=0, x=0.

S

A: "I don't know what to search so I searched i don't know what to search."
B: "You searched i don't know what to search so that's means you know what to search. Liar."

i don't know what to search by Solve that problem! Right now! April 12, 2021

I don't know what to tell you 

A saying that's used to tell someone nicely that nothing is getting done about something,that they simply don't care or that you're "shit out of luck"

Employee: "We have a lot of work and no time to do it" Boss: "I don't know what to tell you"

I don't know what to tell you by battleaxe June 13, 2017

I don't know what to write 

Well clearly that's false.

Write this when you have absolutely no idea what to write.

God I'm bored... Let's open google and search "I don't know what to write"

I don't know what to write by Harikjay February 6, 2019