This topic is not interesting for me, but I have to study it anyway because I have to be able to speak (in) ON different (topic) topicS. Notice that a comma is required after the word "me" because the coordinating conjunction "but" starts a new clause (sentence).

After Richard's corrections, you have a good sentence but there is still room for stylistic improvement. Your sentence is really composed of three complete sentences glued together by two conjunctions: 1. "This topic is not interesting" 2. "I have to study it anyway" 3. "I have to be able to ..." It ends up feeling more like a paragraph than a sentence because none of the three sentences dominates the others. A sentence needs to have a purpose. To fix this, decide which sentence is the one you want to emphasize (I'll use #2). Then turn the other two into subordinate phrases: "Finding this topic uninteresting, I must nonetheless study it to be able to speak on a variety of topics." In this construction, sentence #1 has been turned into an adjective phrase, sentence #3 has been turned into an adverbial phrase ("to be able..."), and #2 is now the single main clause. Try to do this most of the time: for each sentence pick one main subject and verb. Then embellish them with subordinate clauses. Make each sentence say something specific.

Your sentence is understandable, but it could be improved for better grammar and flow. Here's a corrected and more natural version: "This topic isn’t interesting to me, but I have to study it anyway because I need to be able to speak about different topics." Tips for improvement: 1. Prepositions: Use "to" instead of "for" after "interesting." For example: "interesting to me" is correct. 2. Plural nouns: Use "topics" (plural) to match "different topics." 3. Avoid repetition: Replace the second "I have to" with "I need to" for variety. 4. Flow: Combining ideas with natural conjunctions like "but" and adding "about" makes the sentence smoother. Practice tip: When writing or speaking, think about how you can vary sentence structure to avoid repetition. Reading or listening to native speakers' examples on the same subject will also help!