How does one determine he has a learning disability? How does a graduate student determine if he has a learning disability? Are there any signs to look for? At what point is it worth seeking a professional opinion?


Some people, at least, believe there are a significant number of adults who would be identified as having a learning disability if they were children now. Some of these adults are in academia, and have succeeded academically despite their disability, perhaps through developing good coping mechanisms. Never-the-less, it may be that there are other techniques they have not thought of/come across that would benefit them. 

What signs might suggest that this is the case, in a context where past academic success is the norm and future academic success is the expectation?
From http://ldaamerica.org/adults-with-learning-disabilities-an-overview/ :


  Positive characteristics of adults with LD may include problem-solving skills, compensatory strategies, persistence, empathy, and outgoing personalities.  Areas of difficulty include: difficulty with reading, writing and/or math; poor memory; difficulty following directions; inability to discriminate between or among letters, numbers, and/or sounds; eye-hand coordination problems; difficulty putting things in the right sequence;
  disorganization; and/or difficulty adjusting to change.


Determining whether an adult has a Specific Learning Disability (SLD) depends on the type of disability (e.g. Auditory Processing Disorder, Dyscalculia, Dysgraphia, Dyslexia, Language Processing Disorder, Non-Verbal Learning Disabilities, or Visual Perceptual/Visual Motor Deficit).  Each disability will manifest itself differently, and the degree of influence will vary by individual.  In general, you will need a professional to determine whether you have said disability (see http://ldaamerica.org/adult-learning-disability-assessment-process/ ).