Break it into syllables and parts. Let's use your example of "anticollineation" We first separate the prefix "anti-" (anti-collineation) Now we see that it has a "with" prefix in the form of "col" * (anti-col-lineation") We now see that the word is an adaption of the word "linear" (pronunciation: LIN-ee-er), so we know that the /e/ and /a/ in "lineation" are in separate syllables. We can also break off the "-tion" suffix. Now separate into syllables and put the stress on the /a/ (since in "-tion" words, the vowel before the "-tion" generally has the stress), and we get an-ti-col-lin-e-A-tion. * This "with" prefix comes from the Latin word "cum" (meaning: "with"), and takes the form "co-" plus the first letter of the word/stem if the word/stem begins with a consonant. Examples: communication, collaboration, corroboration (note that some words, like "consortium" or "congress", have the prefix "con", which is similar but does not cause doubling of the consonant, because it does not end in a vowel). Basically this is a very long-winded explanation of a pretty simple thing, but being able to identify parts and roots of words is very helpful, even for native speakers. Knowledge of Latin is useful in this regard, so if you want to be able to discern the pronunciation and meanings of long, unfamiliar words (assuming they are Latin-based, which they often are), then look up "Latin roots in English" or some other such phrase online, and you should find a good list.

The simple answer is that you can't. Native English speakers mispronounce words they have read but not heard spoken before. I have not heard of the words above and have no idea what they mean. Anticollineation.- I'm sure you know other words that start with "anti" and any word that ends "ation" has the stress on the "a" /ei/.. I guess the c is a /k/ sound and the o is a schwa. Rhabdomancy. Rh is just an /r/ the mancy will rhyme with fancy. do rhymes with "the". Main stress on first syllable. Just think about other words you know. I could be wrong though!

Pronounce, not pronoun. Any long and complex word in English can be broken into parts which we can recognise (and can pronounce. There are other words which start with "anti-", and others which have endings like "-tion" and "-ancy". So really, even if we don't know the meaning of the word, we can make a fairly good guess at how it's pronounced! Or, you can look for pronunciations. There should be one somewhere. http://howjsay.com/index.php?word=rhabdomancy (Nothing for "anticollineation", but as other members have pointed out, it should be easy enough to guess based on what you already know.)

You can always try www.forvo.com