If you increase eldritch Blast's range to 600 feet because of the invocation and spell sniper. Is it possible to cast it from the view of the pet, an eagle for example, with the voice of the chain master if the target is somewhat behind cover (not full) ? 

My opinion is you’d still have a penalty because even though you could see the target clearly, part of it would still be blocked so you’d only be able to target 1/2 or 1/4 of it depending on how much cover it had. 

Yeah the angle it is being cast at matters more than sight. If you can see the creature with your familiar when your character can't see it, I would say cover still applies. If it is full cover then we have a different conundrum because this is assuming your spells can arc around the cover. I as a DM would say that while you can see the creature from the point of view as your familiar you can't directly target it. Imagine your familiar was in a complex winding dungeon and the target you want to hit is within 600 feet, the spell likely would not arc all the way through the dungeon to hit that one particular enemy, that idea is way too powerful. My ruling then is that cover depends on the position of your player not your angle of viewing.

Seeing through your pet's eyes take an action and ends at the start of your next turn unless you continue spending an action. In otherwords: you cannot cast Eldritch Blast while seeing through the familiar's eyes unless you had someway to do so as a bonus action. Also spells travel in a straight line unless stated otherwise so even if you could cast there must still be a straight line unobstructed between you and at least part of the creature you're targeting - normally they get their cover bonus based on obstacles between them and the point of origin (you) but thanks to spell sniper you can ignore 1/2 and 3/4 cover. Still, if they had total cover from you (the point of origin of the spell) they cannot be targeted even if they had no cover from your familiar.

Normally it requires an action to see through your familiar’s eyes. But a Pact of the Chain Warlock can take the Voice of the Chain Master Eldritch Invocation which doesn’t specify that it requires an action. 

Quote from Tim >>

Normally it requires an action to see through your familiar’s eyes. But a Pact of the Chain Warlock can take the Voice of the Chain Master Eldritch Invocation which doesn’t specify that it requires an action. 

 While it doesn't specify, it resorts to the wording of the Find Familiar spell which does require an action.

Quote from Tim >>

Normally it requires an action to see through your familiar’s eyes. But a Pact of the Chain Warlock can take the Voice of the Chain Master Eldritch Invocation which doesn’t specify that it requires an action. 

 
It only specifies how it is enhanced: the range is now "same plane of existence" instead of 100 ft. and when you are using the senses thing you can speak through the familiar using your voice.

Jeremy Crawford confirmed this.

https://www.sageadvice.eu/2016/03/20/voice-of-the-chain-master-familiar/

Voice of the Chain Master enhances the find familiar spell, which otherwise works as written for the warlock.