Learn Farsi: تا جایی که من خبر دارم، این حد دانش ماست. - As far as I know, this is the limit of our knowledge.

Unlike many other conjunctions you have learned that trigger the subjunctive (like 'so that' or 'before'), تا جایی که (meaning 'as far as' or 'to the extent that') deals with established facts or reality. Because you are stating the actual extent of what you currently know, it is followed by the regular present indicative خبر دارم.

Could I use the verb می‌دانم (I know) instead of خبر دارم in this phrase?

You would be understood, but تا جایی که من خبر دارم (literally 'to the extent that I have news' or 'am informed') is a very common set phrase in Farsi. Native speakers strongly prefer this over using می‌دانم when saying 'as far as I know'.

Where is the verb 'is' in the second half of the sentence?

It is attached to the very end! The word ماست is a contraction of the pronoun ما (mâ, meaning 'us' or 'our') and the 'to be' verb است (ast, meaning 'is'). The 'a' sound drops out, blending them into a single word.

How do the words connect in the phrase حد دانش ماست?

They are connected by the Ezafe, the hidden 'e' sound that links nouns to other nouns or adjectives. It is pronounced as had-e dânesh-e mâst. This literally strings together as 'the limit (of) knowledge (of) us-is', which gives us 'is the limit of our knowledge'.