Memorize the articles! Follow the gender of the noun that it's describing.
Diese -> Die. // Dieses -> Das. // Dieser -> Der. //
Notice that the ending is the same, so remember the article of the noun that follows, and you'll get it. Taking the the exercise as an example, "das Kind", therefore it's "dieses Kind" You can also check the grammar section of each lesson, you'll learn a LOT
The program said to type what you hear. Included in the German statement was a personal name - "Anna" which I spelled as Ana. Either spelling is correct when one is dealing with a personal name. If the remainder of the sentence is correct, one should not be marked wrong over the spelling of a given name. This should be corrected.
just did a deep dive myself to determine when to use dies vs dieses for the demonstrative pronoun
diese and dieser are the nominative feminine and masculine forms respectively, and generally you can use either use dies or dieses for the neuter.
in some cases you will want to use one over the other but i think for this lesson it probably suffices to accept that they are both fine
personally i found the Wiktionary entry very enlightening. cheers!
Although the difference between dies and jenes (this and that) is sometimes confounded in spoken language, there is no doubt, that Raisinnoir is right. Dieses is this. If you are regarding only one language there is sometimes the possiblity to substitute jenes by dieses. This may sound sometimes smoother even if jenes would be more correct for the situation.