When presenting your claim in an argument, one good way to make it stronger against a counterclaim is to

be dramatic in your delivery of the claim
compare your claim to claims from other arguments
dismiss the counterclaim as a fallacy
present research that disproves the counterclaim

he can attribute his excellent skills in karate to his commitment to practice and discipline.

select the correct meaning of the word attribute.

glean
assign
credit
deny

to support your claim and present a strong argument, you should always include

evidence
diagnoses
pathos
scenarios

For the first question, the answer would be the last option. One good way to make it stronger against a counterclaim is to present research that disproves the counterclaim. Showing research would show that your claim is plausible and it will be a very good foundation in your argument. For the second question, the correct answer would be credit. Attribute in the sentence is used as a verb where his excellent skills should be in regard to his commitment. For the third query, the correct answer would be the first option. In order to support your claim and present a strong argument, you should always include evidences since it plays a big role in giving reliability in your argument.