Question

I ------- go to the party tonight what I am not sure fill with proper modal​

Answer 1

The blank in the given sentence should be filled with the modals as shown and explained below:

I may/might go to the party tonight but I am not sure.

Explanation

'May' and 'Might' are the modals of probability. So when we talk about the probability and possibility of an action and are not sure about it, we use any of the modals mentioned above.  

Answer 2

MODALS

Verbs which tell us about the probability, ability, obligation etc. are known as modals or modal verbs. They are different from the regular verbs we use in English.

List of some common used Modals :-

• Can/Could
• May/Might
• Shall/Should
• Will/Would
• Must

Now, back to your question :-

I may/might go to the party tonight but I am not sure.

Since, the question mentioned itself that I am not sure for the party, therefore, the modals which expresses probability will be used above.

Some more examples of modals in sentences :-

• I will attend the meeting tomorrow.
• The train shall reach here by 5:00 P.M.
• Catherine must come today.
• Liam might announce his plans today.
• I can draw your portrait.