calling a function which takes a dictionary as argument

[Mekire]

You don't need to use the **kwarg syntax to just pass a dict to a function.
**kwarg is used for passing a number of keyword arguments. Any keyword arguments the signature doesn't explicitly handle are put in the kwarg dict doing this.

anyway... this is all you need:

dic = {3:0.2, 4:0.5, 5:0.1, 6:0.8, 7:0.34}
 
def function(dic):
   if not dic:
      return dic
   else:
      dic[100] = 0.1
      return dic
 
function(dic)
print(dic[100])