There are many ways to fix every single one of these sentences. These are some suggestions:

1) {the way you have corrected it is fine}
2) It is much fine today.--> It is better today/Today is a finer day than yesterday (was). (Depends on what you want to say)
3) Paris is a worth-seeing city.--> Paris is worth seeing/Paris is a city worth seeing/visiting
4) My friends both sisters are doctors.--> Both of my friends' sisters are doctors.
5) Mike is greater than any student in the class.--> Mike is the best student in class. (Comparing more than two elements so superlative should be used)

6) Shakuntala is better than any drama in Sanskrit.-->Shakuntala is the best Sanskrit drama in the world.
7) The later suggestion is better than the former.--> The latter suggestion is better than the former (one) (is).
8) Little learning is a dangerous thing.-->OK
9) Her Birthday is the most happiest even this year.--> (ok except for the typo-should be event)
10) Usually the rich people hate poor. --> ...rich people hate poor people/...the rich hate the poor.
11) Go and meet the concerned clerk in the university. --> (do you mean the clerk is concerned- this can be a strange modifier mistake)

Thanks Issac for clearing the doubts. I still have some doubts in following sentences.

8) Little learning is a dangerous thing.-->OK

Here I think "little learning" implies a small amount of learning. Now little (without preceded by an article) usually have negative meaning so "little learning" is implying hardly any or not much. But "little learning" here implies some learning so i think l think little should be preceded by article A. So IMO sentence should be:
A Little learning is a dangerous thing.

9) Her Birthday is the most happiest even this year.--> (ok except for the typo-should be event)

Here since happiest is the superlative form of happy so i think most is not needed before happiest.

11) Go and meet the concerned clerk in the university. --> (do you mean the clerk is concerned- this can be a strange modifier mistake)

Here i think concerned used as an adjective of clerk is means relevant. But i couldn't find any flaw in this sentence

Please correct if i'm wrong in any of the above sentences.

Thanks
Tarun

Hi Tarun,

Absolutely right about the following. Little has the connotation and meaning of not a lot and the sentence's meaning is more along the lines of a little bit of learning in the more positive sense, so the article 'a' would be appropriate.

8) Little learning is a dangerous thing.-->OK

Here I think "little learning" implies a small amount of learning. Now little (without preceded by an article) usually have negative meaning so "little learning" is implying hardly any or not much. But "little learning" here implies some learning so i think l think little should be preceded by article A. So IMO sentence should be:
A Little learning is a dangerous thing.

For this one, exactly right: the word 'most' is completely wrong here as we have the superlative happiest.

9) Her Birthday is the most happiest even this year.--> (ok except for the typo-should be event)

Here since happiest is the superlative form of happy so i think most is not needed before happiest.

Finally, in this one, the only thing I would say is to replace the preposition 'in' with 'at'; as for the concerned clerk, it works grammatically because concerned is the adjective to clerk, but the meaning can be awkward.

11) Go and meet the concerned clerk in the university. --> (do you mean the clerk is concerned- this can be a strange modifier mistake)