Ok i just wants to meke sure if this is grammatically correct.

Here is the phrase:

"The personal growth throughout one's life"
or is it
"The personal growth throughout ones life"
or is it
"The personal growth throughout ones' life"

I know basic possessive rules. But I'm confused on this one however

The first one is correct.

https://brians.wsu.edu/2016/05/19/ones-ones/

To determine which option is grammatically correct, let's break it down and understand the rules for possessives:

When you want to show possession or indicate that something belongs to someone, you typically use an apostrophe ('s) followed by an "s" after the person or entity that possesses something. For example: "John's car" or "the company's success."

In your case, the phrase is referring to personal growth throughout someone's life. Since "one" is a pronoun referring to a person in a general sense, you can use the possessive form with an apostrophe ('s) to indicate this.

So, the correct option is: "The personal growth throughout one's life."

Please note that "ones" is the plural form of "one," so it would not be appropriate to use it in this context. Additionally, "ones'" would indicate possession by multiple people, which is not what you intend to express in this particular phrase.