Performance tuning in DB2 aims to enhance query execution speed by optimizing various aspects such as indexes, database design, and configuration parameters to improve overall system performance. 

A Unique Constraint in DB2 ensures data integrity by enforcing uniqueness in a specific column or combination of columns, ensuring that each value in the column(s) is unique across the table. This constraint prevents duplicate entries, ensuring data accuracy and consistency. Therefore, the correct option is a Unique Constraint. Primary Key also enforces uniqueness but additionally implies uniqueness and not nullity, making Unique Constraint a more general answer for ensuring uniqueness. 

Scrollable cursors would be the most efficient choice for traversing result sets in both forward and backward directions. Scrollable cursors allow data to be accessed in any direction (forward or backward) and at any row within the result set, providing the flexibility needed for efficient navigation during report generation. Unlike forward-only cursors, scrollable cursors enable bidirectional movement through the result set without the need to re-query the database. 

The XML Declaration in DB2 specifies the version of the XML standard being used. It typically appears at the beginning of an XML document and declares the XML version number (e.g., '1.0' or '1.1'). This declaration ensures that parsers interpret the document correctly according to the specified XML version. 

When selecting a clustering key, a DBA should consider factors such as the distribution of data values, the uniqueness of the key, and the access patterns of the queries. A clustering key should ideally distribute data evenly across the table to prevent hot spots, ensure uniqueness to avoid duplicates, and align with common query patterns to optimize query performance. 

Range partitioning in DB2 involves dividing data based on specified key values. It allows for the organization of data into logical ranges, enabling efficient querying and maintenance operations. 

The correct DB2 command used to restore a database from a backup is "RESTORE DATABASE." This command allows DBAs to restore a database from a previous backup, whether it's a full database backup or incremental backup. It's a critical step in the database recovery process and is essential for restoring databases in case of data loss or corruption. 

When a column is defined with a NOT NULL constraint, DB2 rejects any attempt to insert NULL values into that column. This ensures data integrity by enforcing the rule that the column must have a value for every row. 

XML or JSON data in DB2 represents semi-structured data. Semi-structured data combines aspects of both structured and unstructured data, allowing for flexibility in data organization while still maintaining some level of schema or format. XML and JSON are commonly used formats for representing semi-structured data due to their flexibility and widespread adoption in modern application development. 

The correct option is Option 1: Timestamp. Point-in-time recovery in DB2 enables the recovery of data to a specific timestamp, allowing users to restore the database to a particular moment in time, ensuring data consistency and integrity.