heaven only knows
Maybe God knows but I don't know and no one else knows. Often used with only.
Do you know where Susan is? God only knows!
Goodness knows, the poor man needs the money.
Heaven only knows, I have tried hard enough.
a little knowledge is a dangerous thing
A person who knows a little about something may think he knows it all and make bad mistakes. A proverb.
John has read a book on driving a car and now he thinks he can drive. A little knowledge is a dangerous thing.
before you know it
Sooner than one would expect.
Don't despair; we'll be finished with this work before you know it!
feel in one's bones
know in one's bones
To have an idea or feeling but not know why.
I feel in my bones that tomorrow will be a sunny day.
I know in my bones that God will protect us.
for all one knows
According to the information one has; probably.
For all we know, Ron and Beth might have eloped and been married in a French chateau.
in the know
Knowing about things that most people do not know about; knowing secrets or understanding a special subject.
Tina helped Professor Smith make some of the exam questions, and she felt important to be in the know.
In a print shop, Mr. Harvey is in the know, but in a kitchen he can't even cook an egg.
know a thing or two about
To be experienced in; have a fairly considerable knowledge of.
Иметь опыт в чем-либо; иметь существенные знания о чем-либо.
Tom has dealt with many foreign traders; he knows a thing or two about stocks and bonds.
Jack has been working as a mechanic for years, and he knows a thing or two about cars.
Джек работал механиком долгие годы, и он понимает, что к чему в машинах.
know by sight
know someone by sight
This idiom is used when the person has been seen previously but is not known personally.
Знать кого-либо в лицо; быть поверхностно знакомым с кем-либо.
I can't say that I know Lily well, actually I know her by sight only.
Я не могу сказать, что я знаю Лили хорошо, на самом деле я знаю только как она выглядит.
I have never met our new neighbors; I simply know them by sight.
The woman said that she would know the thief by sight if she ever saw him again.