Well, yes, in lot of textbooks (like Lambdin's Lehrbuch Bibel-Hebräisch and dictionaries (like Gesenius Hebräisches Handwörterbuch) the cantillation mark עוֹלֶה is used for this purpose. I prefer always noting in writing word stress when not on the ultimate as a memnotic exercise. My Langenscheidts Handwörterbuch Hebräisch-Deutsch uses the מֶתֶג like in מֶֽלֶךְ, which is maybe more mainstream. Being a cantillation sign, this is of course restricted to Hebrew.
Well, to express this is or that is, i.e. the independent demonstrative pronoun, Hebrew does not have two different sets like English for distal and proximal things. But if you want to modify a noun, then you can say הַתַּפּוּחַ הַהוּא that apple in higher registers of language.
As far as I understand it now, there were originally two words in the Tanakh, the collective noun יֶ֫רֶק, which meant greenery, vegetation or herbiage, and יָרָק, which meant vegetable or greens. The latter gained in Middle Hebrew the plural יְרָקוֹת. As you mostly speak of vegetables in the plural, people began to confuse the two words and started using יֶ֫רֶק as the singular for vegetable and this stuck. PS. Edited.
IF you mean that you got a word-bank exercise that lacked the word "a", then your translation would be "This is not vegetable", as in "This is not vegetable matter" or "This is not vegetation". I see that Morfix defines "יֶרֶק" formally as "vegetation, herbage, greenery" and colloquially as "vegetable".
IF you mean "where is the indefinite article in the Hebrew sentence":
There is no indefinite article in Hebrew, so when a Hebrew noun is not definite, we translate it as indefinite, using "a" or "an" as appropriate. This is explained in the Tips for the first skill, Letters 1, which are accessed from the website (not available from the mobile apps). The direct link is