Hi Harjeet,

I have tried your code in my Org and found that the value of the 'selected' of wrapper named wrapAgent is always set to false and due to this 'userSetId' set is not updating with the userId which you are further using in your 'For loop'. 
You can set it to true as I did or you can dynamically set the 'true' or 'false' for different scenarios as per your requirement. Below code is giving 92% code coverage in my Org. 
Also, In the test class you need to set the value of name as 'TeleSales Queue' instead of 'test group' while inserting the Group.

Apex class : 

public class TodayTelesalesDetails {
    
    public Date Today { 
        get { 
            return Date.today(); 
        }
    }
    public List<wrapAgent> wrapAgentList{get; set;}
    public List<User> selectedAgents{get;set;}
    
    public TodayTelesalesDetails (){
        
        if(wrapAgentList == null) {
            wrapAgentList = new List<wrapAgent>();
            
            for(User teleSalesAgent: [select Id, Name, Email from User where Name IN('Steve Waugh','Yuvraj Singh')]) {
                // As each agent is processed we create a new wrap object and add it to the wrapAgentList
                wrapAgentList.add(new wrapAgent(teleSalesAgent));
            }
        }
    }
    
    public PageReference doFullSave(){
        
        set<id> userSetId = new set<id>();
        list<GroupMember> gmm = new list<GroupMember>();
        List<GroupMember> toBeDeleted= [SELECT Id, GroupId, UserOrGroupId FROM GroupMember where GroupId = '00G9D000000toPYUAY'];
        delete toBeDeleted;
        List<User> userlist=[select Id, Name from User where Name IN('Steve Waugh','Yuvraj Singh')];
        
        for(User u : userlist)
        { 
            system.debug('message3>>'+u);
            for(wrapAgent wrapAccountObj : wrapAgentList) {
                
                if(wrapAccountObj.selected == true) {
                    userSetId.add(wrapAccountObj.teleAgent.id);
                    
                }
            }
            
        }
        
        for(User us : [select id from User where id IN : userSetId])
        {
            
            for(Group gg : [select id,name from Group where type = 'Queue' and Name = 'TeleSales Queue'])
            {
                GroupMember gm = new GroupMember();
                gm.groupId = gg.id;
                gm.UserOrGroupId = us.Id;
                gmm.add(gm);
            }
            
        }
        
        
        insert gmm;
        PageReference pageRef = new PageReference('/');
        pageRef.setRedirect(true);
        return pageRef;
    }
    
    
    
    public PageReference doCancel(){
        
        PageReference pageRef = new PageReference('/');
        pageRef.setRedirect(true);
        return pageRef;
    }
    
    
    public class wrapAgent{
        public User teleAgent {get; set;}//Please put the custom metadata names
        public Boolean selected {get; set;}
        
        
        //This is the contructor method. When we create a new object we pass a telesales metadata member that is set to the acc property. We also set the selected value to false
        public wrapAgent(User teleSalesAgent) {
            teleAgent = teleSalesAgent;
            selected = true;   // assigning value true
         // selected = false;
        }
    }
}

============================================================
Test class :

@isTest
public class Test_TodayTeleSalesDetails {
    
    public static testMethod void validateusersinqueue() {
        Group testGroup = new Group(Name='TeleSales Queue', Type='Queue');   //give the name as TeleSales Queue
        insert testGroup;
        
        Profile p = [SELECT Id FROM Profile WHERE Name='Standard User']; 
        User u = new User(Alias = 'standt', 
                          Email='standarduser@testorg.com', 
                          EmailEncodingKey='UTF-8', 
                          FirstName='Steve ', 
                          LastName= 'Waugh',
                          LanguageLocaleKey='en_US', 
                          LocaleSidKey='en_US', 
                          ProfileId = p.Id, 
                          TimeZoneSidKey='America/Los_Angeles', 
                          UserName='YATest@test.com');
        Insert u;
        
        Test.startTest();
        TodayTelesalesDetails telesalesDetails=new TodayTelesalesDetails();
        telesalesDetails.doFullSave();
        telesalesDetails.doCancel();
        Test.stopTest();
    }
}

I hope you find the above solution helpful. If it does, please mark as Best Answer to help others too.

Thanks and Regards,
Ajay Dubedi
www.ajaydubedi.com