Hey Aspirant, 

For getting a FEE waiver by showing your parents income less than 1 Lakhs, you need documents like :

• Caste Certificate 
• Income Certificate from Panchayat, Zila Parishads, District Council or District Court of your area. 
• Admission documents given by Jossa And University 
• JEE Scorecard
• 10th and 12th Marksheet 

For Format of Income Certificate for NIT, refer this link :

https://josaa.nic.in/webinfocms/Public/View.aspx?page=73

And you're needed to show your Income certificate in some NITs every semester to claim Fee waiver  

Good Luck!!