"Ist das dein Blut?"

Translation: Is this your blood?

[ArguingInElvish]

"Nein," he replied as the door lock clicked, "nicht meins."

[MortiBiRD]

"No" antwortete er als die Tür in das Schloss fiel.

[mizinamo]

"nicht meins" at the end :)

(It's not in front of a noun, so you need the pronoun form, which has endings for nominative singular masculine and neuter.)

[Ryan561372]

How do you ask if somebody is a vampire in German.

[mizinamo]

What do you think? Give it a try!

the vampire = der Vampir

[HelloIAmNoah]

Bist du ein Vampir?

[mizinamo]

Correct :)

[pmukkala174]

Wouldn't it be "Bist du Vampir?" Because maybe being a vampire is a job

[PierFrance262780]

Wow, that was difficult! How did you do, with just such few hints!

[i-d-k]

Sind Sie ein Vampir?

[Rusmir123]

Etwas davon, ja.
Did I get it? "Some of it, yeah." from Fight Club

[madjerT]

Shouldn't "Is that your blood" be accepted. It wasnt

[mizinamo]

"Is that your blood?" is one of the accepted translations.

Did you, perhaps, have a listening exercise rather than a translation exercise? If not, do you have a link to a screenshot?

[yaboibiko]

"I'd like to return it." he continued, after which he gave the blood back.

[Don2077]

Why not "Ist diese dein Blut"?

[mizinamo]

Why not "Ist diese dein Blut"?

When we introduce something new to the conversation, we use neuter singular, dies or das.

Thus Ist das dein Blut?

[EdTyrone]

So, "Ist dies dein Blut?" an acceptable statement, or would Germans prefer to use "das" in this example. And, why one over the other?

[mizinamo]

So, "Ist dies dein Blut?" an acceptable statement

Yes.

would Germans prefer to use "das" in this example

Yes.

das is pretty widely used to introduce new material, whether it's "close" or "far".

If you must distinguish, I'd be more likely to use das hier and das da rather than dies and das.

(And jenes is completely old-fashioned. It's not much more used than "yon picture" would be in English.)