My groundnut leaves are turning yellow all over while soil looks okay, which nutrient and what spray?

In groundnut, pale yellowing of the young top leaves that shows up worst on the calcareous and high pH lighter patches is most likely iron deficiency chlorosis. Groundnut is well known for this problem on calcareous soils, where there may be plenty of iron in the soil but the high pH locks it up so the plant cannot take it. It appears on the new leaves because iron is immobile, and in bad cases the leaves turn almost whitish. Please confirm with a soil test, and check it is not waterlogging in those patches, which also triggers iron chlorosis. Because soil iron applied to high pH soil is often locked up too, the practical correction is foliar spraying. A common approach in groundnut is spraying ferrous sulphate at roughly a 0.5 to 1 percent solution, sometimes combined with a little citric acid or a chelated iron product, repeated two or three times at about a week apart starting when symptoms first appear. Adjust the concentration and number of sprays to your crop stage and local KVK recommendation, and do not over-apply, because a strong solution will scorch the leaves.