Data model attributes are fields that are added to a dataset from search time field extractions, calculated fields, lookups, or aliases. They can be created within the data model editor or inherited from a parent dataset. They can be edited or removed unless they are required by the data model. They can be added to any type of dataset, not just root search datasets.ReferencesSee About data models, [Define data model attributes], and [Edit data model datasets] in the Splunk Documentation.

The fillnull command replaces null values in one or more fields with a specified value. The values option allows you to specify a comma-separated list of values to fill the null values in the corresponding fields. The fields option allows you to specify a comma-separated list of fields to apply the fillnull command to. The eval statement in the question uses the if and isnull functions to check if field1 and field2 have null values and replace them with 0 and "NO-VALUE" respectively. The equivalent expression using fillnull is to use the values option to specify 0 and "NO-VALUE" and the fields option to specify field1 and field22
1: Splunk Core Certified Power User Track, page 9. 2: Splunk Documentation, fillnull command.

The following commands are used when creating visualizations: geom, geostats, and iplocation.
Visualizations are graphical representations of data that show trends, patterns, or comparisons. Visualizations can have different types, such as charts, tables, maps, etc. Visualizations can be created by using various commands that transform the data into a suitable format for the visualization type. Some of the commands that are used when creating visualizations are:
* geom: This command is used to create choropleth maps that show geographic regions with different colors based on some metric. The geom command takes a KMZ file as an argument that defines the geographic regions and their boundaries. The geom command also takes a field name as an argument that specifies the metric to use for coloring the regions.
* geostats: This command is used to create cluster maps that show groups of events with different sizes and colors based on some metric. The geostats command takes a latitude and longitude field as arguments that specify the location of the events. The geostats command also takes a statistical function as an argument that specifies the metric to use for sizing and coloring the clusters.
* iplocation: This command is used to create location-based visualizations that show events with different attributes based on their IP addresses. The iplocation command takes an IP address field as an argument
* and adds some additional fields to the events, such as Country, City, Latitude, Longitude, etc. The iplocation command can be used with other commands such as geom or geostats to create maps based on IP addresses.

The statement that fields extracted using the Field Extractor persist as knowledge objects is true. The Field Extractor (FX) is a graphical tool that allows you to extract fields from raw events using regular expressions or delimiters. The fields extracted by the FX are saved as knowledge objects that can be used in future searches or shared with other users.

Using the export function, you can export search results as XML or JSON2. The export function allows you to save your search results in a structured format that can be used by other applications or tools2. You can use the output_mode parameter to specify whether you want to export your results as XML or JSON2. Therefore, options A and B are correct, while options C and D are incorrect because they are not formats that you can export your search results as.