Which sentences are correct?

1) Are you able to assist me on this matter? I would appreciate your assistance on this matter.
OR
2) Are you able to assist me in this matter? I would appreciate your assistance in this matter.

Thanks.

All are correct.

The first sentence in each pair asks a straight question. Under some circumstances it could be considered too direct.

The second sentences are more formal and more polite.

If a collegue is willing to assist, in a form of formal letter how do you respond?

Ah, the eternal battle between "on" and "in"! Both sentences are correct, my friend. It ultimately boils down to personal preference. Some people prefer to use "on" when they want assistance about a specific matter, while others opt for "in" when they want assistance within a particular matter. So, go ahead and pick the one that tickles your fancy. Just make sure not to choose both at the same time unless you want to confuse people and make them wonder if there's a hidden circus act involved.

Both sentences are grammatically correct, but there is a slight difference in meaning.

Sentence 1: "Are you able to assist me on this matter? I would appreciate your assistance on this matter."
In this sentence, "on" is used to indicate the topic or subject of the assistance. It suggests that the assistance is specifically related to the matter being mentioned.

Sentence 2: "Are you able to assist me in this matter? I would appreciate your assistance in this matter."
In this sentence, "in" is used to indicate involvement or participation. It suggests that the assistance is being sought within the context of the matter.

Both prepositions, "on" and "in," can be used in different contexts. The choice between them depends on the exact meaning you want to convey.

Both sentences are grammatically correct, but there is a slight difference in meaning between using "on" and "in" in this context.

1) "Are you able to assist me on this matter? I would appreciate your assistance on this matter."
This sentence suggests that you are asking for someone's help or support specifically related to this matter. The word "on" implies being focused or working directly on something.

2) "Are you able to assist me in this matter? I would appreciate your assistance in this matter."
This sentence also asks for help or support, but it implies being involved or participating in this matter rather than just focusing on it. The word "in" suggests being a part of a situation or process.

So, which option to choose depends on what you specifically want to convey. If you want to emphasize someone's direct assistance in this matter, then the first option using "on" would be more suitable. If you want to highlight their involvement or participation in this matter, then the second option using "in" would be a better choice.