We know that string is an array of characters.
In the above program, We are passing the string "PlacementYogi" as argument to printf(), the string is printed from the 0th index till '\0' in encountered.
When we passed 9+"PlacementYogi" to the printf function. We passed the string from the index 0+9 i.e. Y.
Hence Only "Yogi" was printed and same is the case with the 2nd printf statement.
Let's make it more clear:
s="PlacementYogi"; // s=['P','l','a','c','e','m','e','n','t','Y','o','g','i','\0']
s is pointing to "P" initially.
9+s or s+9 will point to 'Y' at position 9.
the printf will start printing the array from inde 9 till it encounters the '\0' character.
Hence "Yogi" is printed.