"Where is grandfather?"
It's a regional difference. The standard Ukrainian language is based on central dialects, where the form is дід is used.
We also use 'дідо', дідусь', 'дідуньо' for 'grandfather'. (The latter two are diminutive forms of 'дідо'.)
The word 'дід' in Ukrainian can also mean an 'old man', and can be construed as derogatory to 'an older man who one dislikes'.