This is the 676th most frequent Czech word.
majitel
Owner.
Here, 'majitel' is used in its base singular form to denote the owner (person who possesses) of a specific entity, the shop.
Majitel obchodu se stará o své zákazníky.
The owner of the shop takes care of his customers.
'Majiteli' (plural form) denotes possessors or owners, and is used to ask about the intention to obtain ownership.
Chcete se stát majiteli této nemovitosti?
Do you want to become the owners of this property?
'Majitelem' is in the instrumental case, referring to the owner (person possessing the dog) being accompanied.