Hi Manju, 

You need to grab the opportunity Ids from the for loop and run a SOQL outside of your for loop to get the required information. I am posting here a sample code and highlighting the said part 
 

trigger CreateQLI on CQuote__c (after insert,after update) {
    Set<Id> opportunityIds = new Set<Id>();
    List<CQuote__c>quotelist=new List<CQuote__c>();
    for(CQuote__c q : Trigger.new)
    {
        if(q.QOpp_Name__c != NULL)
        {
            opportunityIds.add(q.QOpp_Name__c);
            quotelist.add(q);
        }
    }
    Map<Id, COpportunity__c> oppsWithLineItems = new Map<Id, COpportunity__c>([SELECT Id,(select id,CurrencyIsoCode,Opportunity__c,Principal_Name__c, Product_Category__c,Product_Description__c,
                        Product__r.name,Quantity__c,Unit_Price__c from Opportunity_LineItems__r)from COpportunity__c WHERE Id IN :opportunityIds]);

    if(opportunityIds.size() > 0)
    {
        // Loop through Quotes
        List<Quote_Line_Item__c > quoteItemsForInsert = new List<Quote_Line_Item__c >();
        for(CQuote__c o : quotelist)
        {
            // For each Quote get the related opportunity and line items, loop through the line items and add a new quote line item to the quote line item list for each matching opportunity line item
            COpportunity__c oppWithLineItem = oppsWithLineItems.get(o.QOpp_Name__c);
            for(Opportunity_LineItem__c oli : oppWithLineItem.Opportunity_LineItems__r)
            {
                quoteItemsForInsert.add(new Quote_Line_Item__c(
                        Quote_Name__c=o.id,
                        Product_Name__c=oli.Product__r.name,
                        Principal_Name__c=oli.Principal_Name__c,
                        Product_Category__c=oli.Product_Category__c,
                        CurrencyIsoCode=oli.CurrencyIsoCode,
                        Unit_Price__c=oli.Unit_Price__c
                ));
            }
        }
        // If we have order line items, insert data
        if(quoteItemsForInsert.size() > 0)
        {
            insert quoteItemsForInsert;
        }
    }


    
}

Let me know if this helps, if it does, please mark this answer as best so that others facing the same issue will find this information useful. Thank you