[SalesForce] How to pass a query string param to the Controller

The problem with your code is that the apex:param is outside of the apex:actionFunction. Other code looks ok, but it is uclear what changes you have made on it. So i will post here a working example of passing parameter. Try to modify your code based on this template:

Controller:

public with sharing class MyController {
    public String passedParam { get; set; }
    public MyController(){
        // It is important to initialize a string here
        passedParam = '';
    }

    // This method just outputs the passed value
    public void checkParam(){
        System.debug('### passedParam: ' + passedParam);
    }
}

Visualforce Page:

<apex:page controller="test2">

    <!-- Only one form tag for all components -->
    <apex:form>

        <apex:actionFunction name="sendParam" action="{!checkParam}" reRender="none">
            <apex:param name="p1" assignTo="{!passedParam}" value=""/>
        </apex:actionFunction>

        <a href="#" onclick="sendParam('someString')">Send it</a>

    </apex:form>

</apex:page>

Debug output:

USER_DEBUG|[43]|DEBUG|### passedParam: someString

I would start by modifying your code as follows:

Minimal Reproducible Example

Class

    public class myExample {

public List<wrapperClass> products{
    get {
        if(products == null){
            products = new List< wrapperClass >();

            for(product2 p : [select id,name from product2 limit 4]) {
                products.add(New wrapperClass(p));
            }
        }
        return products;
    }
    set;
}


    public PageReference save() {
        try {
            for (wrapperClass w : products) {
                system.debug('The Quantity is: ' + w.ali.Quantity);

            }
        } catch (Exception e) {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.Error, e.getMessage()));
            return null;
        }
        return null;
    }

    public class wrapperClass {
        public Product2 product { get; set; }
        public opportunitylineitem ali { get; set; }

        public wrapperClass(Product2 p) {
            product = p;
            ali = New opportunitylineitem();
        }
    }



    }

VFP

<apex:form id="editForm">

    <apex:pageBlock>
        <apex:pageBlockTable value="{!products}" var="a">
            <apex:column headerValue="quantity">
                <apex:inputField value="{!a.ali.Quantity}" required="true"/>
            </apex:column>
        </apex:pageBlockTable>
    </apex:pageBlock>

    <apex:commandbutton value="save me" action="{!save}" rerender=""/>

</apex:form>