I'll direct you along the path.............
Both are monoprotic and monobasic so the reaction is one to one.
You can calculate the number of moles of nitrous acid (MV = 0.00400 mol). From this you will say the same number of moles of base will be needed to reach the equivalence point, meaning you will need a certain volume of base (mol/M=Vbase = 0.00400 mol/0.200M = 0.0200 L of base added).
OK, consider the reaction:
HNO2 + KOH ---> KNO2 + HOH
A solution of KNO2 is produced! This is a solution of a weak base, NO2-, i.e., the conjugate base of HNO2 .
How many moles of KNO2 ? 0.00400 mol
What is the final volume? 40 + 20 = 60 mL = 0.060 L
What is the concentration of weak base, NO2- ? 0.0040 mol/0.060L = 0.0667 M
OK, now the problem is simplified to finding the pH of a solution of 0.0667 M NO2-.
You can look up in your table the Ka of HNO2, so Kb for NO2-, will be Kw/Ka.
Finally the same old same old tricks..........
Kb = x2/(0.0667-x)......when you get x, you have [OH-] .....which leads easily to pOH....and finally to pH.