You will be required to provide a receipt of the purchase-related to the claim (a photo of the receipt including the item’s brand & model is sufficient).
In case of accidental damage, a repair receipt mentioning the claim-related item as well as the repair price has to be provided (a photo is sufficient). If the item cannot be repaired, a document issued by a repair company mentioning the claim-related item, the cause of the failure, and stating that the item is not repairable has to be provided.
See here for more details on what these documents should include: What information should appear on the repair invoice or on the document proving that the insured item cannot be repaired?
In case of theft, a police report has to be provided.