You can use transform() function of pandas with 'sqrt' as 'func' or a lamda function for square root as 'func'.
Approach 1: Using lambda function
>>> df
c1 c2
0 1 25
1 4 36
2 9 49
3 16 64
>>> df.transform(lambda x:x**0.5)
c1 c2
0 1.0 5.0
1 2.0 6.0
2 3.0 7.0
3 4.0 8.0
>>> df.transform(lambda x:x**0.5).astype(int)
c1 c2
0 1 5
1 2 6
2 3 7
3 4 8
Approach 2: using sqrt function
>>> df.transform('sqrt')
c1 c2
0 1.0 5.0
1 2.0 6.0
2 3.0 7.0
3 4.0 8.0
>>> df.transform('sqrt').astype(int)
c1 c2
0 1 5
1 2 6
2 3 7
3 4 8