How do I recognize the attachment to certain things? How do I know whether I am attached to ceratain things or not ? 
Examples:


When we attached to the taste we will trying to find more &amp; more tasty foods. We can reduce that by getting a simple meal, cutting the extra meals or only taking 2 meals per day like monks.
When we attached to the clothes , we are trying to buy latest/expensive clothes. We can reduce that desire by wearing simple and charm clothes.


The questions is, How do I know whether I am attached to my career , exam results or not ? ( Now I am in the university. I have to work for exams. Sometime I feel , I am attached to exam results) If it is, How do I work without attaching to it ?

I read this answer already: Should I do what I don't want to do ?
How do I know whether I am attached to my career , exam results or not ? 


The evidence for attachment is dukkha (suffering/discomfort/dissatisfaction). In your next sentence you seem to be aware of feeling the attachment (vedana). The answer to your question then lies in how that makes you feel.


  ( Now I am in the university. I have to work for exams. Sometime I feel , I am attached to exam results) If it is, How do I work without attaching to it ?


It's pretty much an either/or deal: You can either attach to a specific outcome, such as exam results, or put your effort into non-attachment according to buddhist dhamma. 

To my understanding you can't do both, which can put us in a bit of a difficult existential quandary: The question whether you should be attached to your studies or not is only for you to determine.

In case you want to develop a buddhist practice, getting into the meditation called anapanasati is a good start. Also, it is a meditation that can yield good consequences for a lifetime. 

This is a good start:

https://www.accesstoinsight.org/lib/authors/ariyadhamma/bl115.html

You will find plenty of discussion/instructions here:

https://buddhism.stackexchange.com/search?q=anapanasati