In the above the name of customer is not given so what shoud we write in sales journal?

Personally speaking if you have granted them credit you should set them up as a customer in your accounting system. If you do not wish to do that you should be able to record it as Misc. Customer.
The entry would be as follows:
Dr. Accounts Receivable $6000
Cr. Sales Revenue $6000
When payment is received:
Dr. Cash
Cr. Accounts Receivable

Hope that helps

July
2 Invested $32,000 cash and $14,000 of equipment in the business
2 Hired a secretary at a salary of $290 per week, payable monthly.
3 Purchased supplies on account $700 (debit an asset account)
7 Paid office rent of $600 for the month
11 Completed a tax assignment and billed client $1,100 for services rendered
12 Received $3,200 advance on a management consulting engagement
17 Received cash of $2,300 for services completed for Ferengi Co.
21 Paid insurance expense $110
30 A count of supplies indicated that $120 of supplies had been used.
30 Paid secretary $1,160 for the month

Not sure about the first one

Salary exp 1257
Cash 1257

Supplies 700
Cash 700

Prepaid expense 600
Cash 600

Not sure about tax one

Not sure

Cash 2300
Service Revenue 2300

I hope these are OK please let me know I am not sure about the rest . I need some advice asap.

July 2 Debit cash for 32,000
Debit Equipment (PP&E) for 14,000
Credit Owner's Equity (Capital) for 46,000

Jul 2 No entry required

Jul 3 Debit Office Supplies (Current Asset) for 700
Credit Accounts Payable for 700

Jul 7 Debit Rent Expense for 600
Credit Cash for 600

Jul 11 Debit Accounts Receivable for 1,100
Credit Service Revenue for 1,100

Jul 12 Debit Cash for 3,200
Credit Unearned Service Revenue for 3,200

Jul 21 Debit Insurance expense for 110
Credit Cash for 110

Jul 30 Debit Office Supplies Expense for 120
Credit Office Supplies for 120

Jul 30 Debit Salaries Expense for 1,160
Credit Cash for 1,160