Can warlock use 2 attacks with eldritch blast at lvl 8

No, eldritch blast is its own standard action

You can only use eldritch blast as a standard action; you can’t use it in place of an attack.

There are a few ways to see this:

Eldritch Blast (Sp):

^{(Complete Arcane, pg. 7)}

The “(Sp)” notation means that eldritch blast is a spell-like ability. The rules for those say

A spell-like ability has a casting time of 1 standard action unless noted otherwise in the ability or spell description.

^{(Player’s Handbook, pg. 180)}

Also,

Invocations and Eldritch Blast: Eldritch blast is an invocation.

^{(Errata for Complete Arcane pg. 8)}

using an invocation is therefore [because it is Sp] a standard action that provokes attacks of opportunity

^{(Complete Arcane, pg. 7)}

You can use eldritch blast multiple times in a round by using Quicken Spell-Like Ability, or by using the eldritch glaive blast shape (Dragon Magic), which turns eldritch blast into a full-round action that attacks as a reach melee weapon once plus one additional time for every 6 BAB you have (equivalent to iteratives in a full attack, but not including any bonus attacks you might have, e.g. from haste), and also allows you to make attacks of opportunity with the eldritch blast (again, as if it were a reach melee weapon).