Data point comments are a feature that allows you to add comments to specific data points in a story. You can use data point comments to provide additional information, context, or feedback on the data. You can also reply to, edit, or delete existing comments. Data point comments are supported for the following models:
Import models
Planning models
Blended models
Data point comments are not supported for live models, such as SAP S/4HANA live model or BPC live model. Therefore, the correct answer is Import planning model and Blended model, as they are the models that support data point comments.
Data point comments are comments that you can add to a specific value in a table or a comment widget. They are similar to commenting on a single cell in Microsoft Excel. Data point comments are associated with the models, which means that they will appear in any story that uses the same model and has the same value in a table or a comment widget1.
Data point comments can be added to the following models:
Import planning model: This is a model that you create by importing data from a file or a database. You can use this model for planning scenarios, such as budgeting, forecasting, or what-if analysis. You can enable data point comments for this model by selecting the Allow Data Point Comments option in the model properties2.
BPC live model: This is a model that you create by connecting to a SAP Business Planning and Consolidation (BPC) system. You can use this model for real-time planning and analysis with BPC data. You can enable data point comments for this model by selecting the Allow Data Point Comments option in the model properties3.
Data point comments cannot be added to the following models:
SAP S/4HANA live model: This is a model that you create by connecting to a SAP S/4HANA system. You can use this model for real-time analysis with SAP S/4HANA data. However, this model does not support data point comments, because it is read-only and does not allow any changes to the data4.
Blended model: This is a model that you create by blending data from two or more models. You can use this model for combining and analyzing data from different sources. However, this model does not support data point comments, because it is derived from other models and does not have its own data.
1: Using Data Point Comments - SAP Learning 2: Creating an Import Planning Model - SAP Learning 3: Creating a BPC Live Model - SAP Learning 4: Creating an SAP S/4HANA Live Model - SAP Learning : [Blending Data from Multiple Models - SAP Learning]

The correct answers are C. Have a clear message and D. Use corporate branding standards.
These are some of the guidelines that SAP recommends you follow when you create a story. According to the course material1, "Your current reporting and dashboard standards will suffice for SAP Analytics Cloud stories. And if you do not have reporting or dashboard standards, this is the perfect time to create them." The course material also suggests that you should "have a clear message and purpose for your story" and "use corporate branding standards to ensure consistency and professionalism"1.
The other options are not mentioned as guidelines in the course material. Option A) Use grouping is a feature that allows you to group data points in a chart or table, but it is not a general design principle. Option B. Avoid pie charts is a common advice for data visualization, but it is not specific to SAP Analytics Cloud stories.
1: Introducing SAP Analytics Cloud Story Design | SAP Training 2

The story option that can help you create a story as a launchpad to other stories is hyperlink. A hyperlink is a link that allows users to navigate from one location to another by clicking on it.
You can use hyperlinks to link widgets, text, or images in a story to other stories in SAP Analytics Cloud, creating a launchpad effect. Input control, linked analysis, and RSS feed are not story options that can help you create a story as a launchpad to other stories; they are options that can help you filter data, link widgets, or display news feeds in a story. Verified [SAP Analytics Cloud - Hyperlinks]

A public dataset is a type of dataset that is shared among different stories. You can use public datasets to create stories or blend data with models. A public dataset has the following properties:
It can be shared among different stories. You can use public datasets in multiple stories without having to import them again.
It cannot be converted to a model. You cannot convert a public dataset to a model. If you want to create a model from a public dataset, you have to import it as a private dataset first.
Its data is not structured in a star schem
a. A public dataset does not have any predefined dimensions or measures. It only has columns and rows of data.
Its data source cannot be changed. You cannot change the data source of a public dataset after you import it. If you want to update the data in a public dataset, you have to import a new file.

The SAP Analytics Cloud mobile app allows users to view and interact with stories, collaborate with colleagues using comments and notifications, and share links to stories via email or other apps. Users cannot create stories, datasets, or models using the mobile app. Verified [SAP Analytics Cloud - Mobile App]