Multiple survey short answer questions on one slide

First, some basic info about data-entry fields and variables:

When you insert a data-entry field (text or numeric), Storyline automatically creates a variable to hold the entry (aka, its value). 

By default, the variables have generic names, such as TextEntry, TextEntry1, TextEntry2, etc.

In the Timeline, you may see multiple fields called "Text Entry." Or some may have numbers after them (for example, "Text Entry 1"). It depends on whether you insert new fields or duplicate an existing one. 

• • For easier programming and troubleshooting, you should give meaningful names to the fields and variables. (For example: "txt-hydrated" for that field, and "v_hydrated" for the associated variable.) 

Storyline also automatically adds a trigger that updates the value of a data-entry variable when the field "loses focus." That means the value updates when the user clicks somewhere outside the field. 

A variable's value can be accessed throughout the course. It doesn't change until a trigger changes it. This means you can display the value or use it in a trigger condition.

In your case, you don't want the user to advance until they have entered something in each text-entry field. So you could edit the NEXT button's trigger with conditions that check whether each variable has an entry (that is, is not equal to blank). Otherwise ("else"), show a layer (or a shape) with a warning explaining that the user has to enter something in all of the fields. The trigger would look something like this: 

Note: The trigger could be added to a "Save answers" button instead, with other programming preventing the user from advancing. This post has more info about controlling the NEXT button: TIP: Controlling the NEXT Button 101 - Articulate Storyline Discussions - E-Learning Heroes

It’s worth the effort to learn about variables and trigger conditions, because they provide the real power in Storyline. Here’s the User Guide info:

• https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-variables
• https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-work-with-triggers#conditions

Final note: You referred to this as "multiple survey short answer questions." A text-entry (short answer or essay) Survey question can only have one entry. For each answer you want to capture, you need to create a standard Survey question and associate it with a Results slide to enable Storyline to submit the answer to an LMS/LRS.