How to get variable from another function?

Make that variable as global here is the tutorial to do this https://codex.www.ads-software.com/Global_Variables

Try using public properties.
https://php.net/manual/en/language.oop5.properties.php
Example

class MyClass {

	public $name;
	public $email;
	public $text;

	function cl_validate() {
		if ( isset( $_GET['cl_name'] ) && !empty( $_GET['cl_name'] ) ) : $this->name = $_GET['cl_name'];
		endif;
		if ( isset( $_GET['cl_email'] ) && !empty( $_GET['cl_email'] ) ) : $this->email = $_GET['cl_email'];
		endif;
		if ( isset( $_GET['cl_text'] ) && !empty( $_GET['cl_text'] ) ) : $this->text = $_GET['cl_text'];
		endif;
	}

	function cl_send() {

		// sets properties
		$this->cl_validate();

		// use properties in this function
		$name = $this->name;
	}

}

Thanks, this helped!